Merge: * use upstream servers directly for the internal DNS resolver

Close #1212

* Server.Start(config *ServerConfig) -> Start()
+ Server.Prepare(config *ServerConfig)
+ Server.Resolve(host string)
+ Server.Exchange()
* rDNS: use internal DNS resolver
- clients: fix race in WriteDiskConfig()
- fix race: move 'clients' object from 'configuration' to 'HomeContext'
    Go race detector didn't like our 'clients' object in 'configuration'.
+ add AGH startup test
    . Create a configuration file
    . Start AGH instance
    . Check Web server
    . Check DNS server
    . Wait until the filters are downloaded
    . Stop and cleanup
* move module objects from config.* to Context.*
* don't call log.SetLevel() if not necessary
    This helps to avoid Go race detector's warning
* ci.sh: 'make' and then run tests

Squashed commit of the following:

commit 86500c7f749307f37af4cc8c2a1066f679d0cfad
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 18:08:53 2019 +0300

    minor

commit 6e6abb9dca3cd250c458bec23aa30d2250a9eb40
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 18:08:31 2019 +0300

    * ci.sh: 'make' and then run tests

commit 114192eefea6800e565ba9ab238202c006516c27
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 17:50:04 2019 +0300

    fix

commit d426deea7f02cdfd4c7217a38c59e51251956a0f
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 17:46:33 2019 +0300

    tests

commit 7b350edf03027895b4e43dee908d0155a9b0ac9b
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 15:56:12 2019 +0300

    fix test

commit 2f5f116873bbbfdd4bb7f82a596f9e1f5c2bcfd8
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 15:48:56 2019 +0300

    fix tests

commit 3fbdc77f9c34726e2295185279444983652d559e
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 15:45:00 2019 +0300

    linter

commit 9da0b6965a2b6863bcd552fa83a4de2866600bb8
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 15:33:23 2019 +0300

    * config.dnsctx.whois -> Context.whois

commit c71ebdbdf6efd88c877b2f243c69d3bc00a997d7
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 15:31:08 2019 +0300

    * don't call log.SetLevel() if not necessary

    This helps to avoid Go race detector's warning

commit 0f250220133cefdcb0843a50000cb932802b8324
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 15:28:19 2019 +0300

    * rdns: refactor

commit c460d8c9414940dac852e390b6c1b4d4fb38dff9
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 14:08:08 2019 +0300

    Revert: * stats: serialize access to 'limit'

    Use 'conf *Config' and update it atomically, as in querylog module.
    (Note: Race detector still doesn't like it)

commit 488bcb884971276de0d5629384b29e22c59ee7e6
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 13:50:23 2019 +0300

    * config.dnsFilter -> Context.dnsFilter

commit 86c0a6827a450414b50acec7ebfc5220d13b81e4
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 13:45:05 2019 +0300

    * config.dnsServer -> Context.dnsServer

commit ee35ef095ccaabc89e3de0ef52c9b5ed56b36873
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 13:42:10 2019 +0300

    * config.dhcpServer -> Context.dhcpServer

commit 1537001cd211099d5fad01696c0b806ae5d257b1
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 13:39:45 2019 +0300

    * config.queryLog -> Context.queryLog

commit e5955fe4ff1ef6f41763461b37b502ea25a3d04c
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Tue Dec 10 13:03:18 2019 +0300

    * config.httpsServer -> Context.httpsServer

commit 6153c10a9ac173e159d1f05e0db1512579b9203c
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Mon Dec 9 20:12:24 2019 +0300

    * config.httpServer -> Context.httpServer

commit abd021fb94039015cd45c97614e8b78d4694f956
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Mon Dec 9 20:08:05 2019 +0300

    * stats: serialize access to 'limit'

commit 38c2decfd87c712100edcabe62a6d4518719cb53
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Mon Dec 9 19:57:04 2019 +0300

    * config.stats -> Context.stats

commit 6caf8965ad44db9dce9a7a5103aa8fa305ad9a06
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Mon Dec 9 19:45:23 2019 +0300

    fix Restart()

... and 6 more commits

home/helpers.go

@@ -16,7 +16,6 @@ import (
 	"syscall"
 	"time"
 
-	"github.com/AdguardTeam/dnsproxy/upstream"
 	"github.com/AdguardTeam/golibs/log"
 	"github.com/joomcode/errorx"
 )
@@ -118,7 +117,7 @@ func postInstall(handler func(http.ResponseWriter, *http.Request)) func(http.Res
 			return
 		}
 		// enforce https?
-		if config.TLS.ForceHTTPS && r.TLS == nil && config.TLS.Enabled && config.TLS.PortHTTPS != 0 && config.httpsServer.server != nil {
+		if config.TLS.ForceHTTPS && r.TLS == nil && config.TLS.Enabled && config.TLS.PortHTTPS != 0 && Context.httpsServer.server != nil {
 			// yes, and we want host from host:port
 			host, _, err := net.SplitHostPort(r.Host)
 			if err != nil {
@@ -273,14 +272,8 @@ func customDialContext(ctx context.Context, network, addr string) (net.Conn, err
 		return con, err
 	}
 
-	bindhost := config.DNS.BindHost
-	if config.DNS.BindHost == "0.0.0.0" {
-		bindhost = "127.0.0.1"
-	}
-	resolverAddr := fmt.Sprintf("%s:%d", bindhost, config.DNS.Port)
-	r := upstream.NewResolver(resolverAddr, 30*time.Second)
-	addrs, e := r.LookupIPAddr(ctx, host)
-	log.Tracef("LookupIPAddr: %s: %v", host, addrs)
+	addrs, e := Context.dnsServer.Resolve(host)
+	log.Debug("dnsServer.Resolve: %s: %v", host, addrs)
 	if e != nil {
 		return nil, e
 	}