Fix #1069 install: check static ip

Squashed commit of the following:

commit 57466233cb
Merge: 2df5f281 867bf545
Author: Andrey Meshkov <am@adguard.com>
Date:   Thu Feb 13 18:39:15 2020 +0300

    Merge branch 'master' into 1069-install-static-ip

commit 2df5f281c4
Author: Andrey Meshkov <am@adguard.com>
Date:   Thu Feb 13 18:35:54 2020 +0300

    *: lang fix

commit b4649a6b27
Merge: c2785253 f61d5f0f
Author: Andrey Meshkov <am@adguard.com>
Date:   Thu Feb 13 16:47:30 2020 +0300

    *(home): fixed issues with setting static IP on Mac

commit c27852537d
Author: Andrey Meshkov <am@adguard.com>
Date:   Thu Feb 13 14:14:30 2020 +0300

    +(dhcpd): added static IP for MacOS

commit f61d5f0f85
Author: Ildar Kamalov <i.kamalov@adguard.com>
Date:   Thu Feb 13 14:13:35 2020 +0300

    + client: show confirm before setting static IP

commit 7afa16fbe7
Author: Ildar Kamalov <i.kamalov@adguard.com>
Date:   Thu Feb 13 13:51:52 2020 +0300

    - client: fix text

commit 019bff0851
Author: Ildar Kamalov <i.kamalov@adguard.com>
Date:   Thu Feb 13 13:49:16 2020 +0300

    - client: pass all params to the check_config request

commit 194bed72f5
Author: Andrey Meshkov <am@adguard.com>
Date:   Wed Feb 12 17:12:16 2020 +0300

    *: fix home_test

commit 9359f6b55f
Merge: ae299058 c5ca2a77
Author: Andrey Meshkov <am@adguard.com>
Date:   Wed Feb 12 15:54:54 2020 +0300

    Merge with master

commit ae2990582d
Author: Andrey Meshkov <am@adguard.com>
Date:   Wed Feb 12 15:53:36 2020 +0300

    *(global): refactoring - moved runtime properties to Context

commit d8d48c5386
Author: Andrey Meshkov <am@adguard.com>
Date:   Wed Feb 12 15:04:25 2020 +0300

    *(dhcpd): refactoring, use dhcpd/network_utils where possible

commit 8d039c572f
Author: Ildar Kamalov <i.kamalov@adguard.com>
Date:   Fri Feb 7 18:37:39 2020 +0300

    - client: fix button position

commit 26c47e59dd
Author: Ildar Kamalov <i.kamalov@adguard.com>
Date:   Fri Feb 7 18:08:56 2020 +0300

    - client: fix static ip description

commit cb12babc46
Author: Andrey Meshkov <am@adguard.com>
Date:   Fri Feb 7 17:08:39 2020 +0300

    *: lower log level for some commands

commit d9001ff848
Author: Andrey Meshkov <am@adguard.com>
Date:   Fri Feb 7 16:17:59 2020 +0300

    *(documentation): updated openapi

commit 1d213d53c8
Merge: 8406d7d2 80861860
Author: Andrey Meshkov <am@adguard.com>
Date:   Fri Feb 7 15:16:46 2020 +0300

    *: merge with master

commit 8406d7d288
Author: Ildar Kamalov <i.kamalov@adguard.com>
Date:   Fri Jan 31 16:52:22 2020 +0300

    - client: fix locales

commit fb476b0117
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Fri Jan 31 13:29:03 2020 +0300

    linter

commit 84b5708e71
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Fri Jan 31 13:27:53 2020 +0300

    linter

commit 143a86a28a
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Fri Jan 31 13:26:47 2020 +0300

    linter

... and 7 more commits

util/helpers.go

@@ -0,0 +1,59 @@
+package util
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"path"
+	"runtime"
+	"strings"
+)
+
+// ---------------------
+// general helpers
+// ---------------------
+
+// fileExists returns TRUE if file exists
+func FileExists(fn string) bool {
+	_, err := os.Stat(fn)
+	if err != nil {
+		return false
+	}
+	return true
+}
+
+// runCommand runs shell command
+func RunCommand(command string, arguments ...string) (int, string, error) {
+	cmd := exec.Command(command, arguments...)
+	out, err := cmd.Output()
+	if err != nil {
+		return 1, "", fmt.Errorf("exec.Command(%s) failed: %v: %s", command, err, string(out))
+	}
+
+	return cmd.ProcessState.ExitCode(), string(out), nil
+}
+
+// ---------------------
+// debug logging helpers
+// ---------------------
+func FuncName() string {
+	pc := make([]uintptr, 10) // at least 1 entry needed
+	runtime.Callers(2, pc)
+	f := runtime.FuncForPC(pc[0])
+	return path.Base(f.Name())
+}
+
+// SplitNext - split string by a byte and return the first chunk
+// Whitespace is trimmed
+func SplitNext(str *string, splitBy byte) string {
+	i := strings.IndexByte(*str, splitBy)
+	s := ""
+	if i != -1 {
+		s = (*str)[0:i]
+		*str = (*str)[i+1:]
+	} else {
+		s = *str
+		*str = ""
+	}
+	return strings.TrimSpace(s)
+}