* /control/dns_config: allow all valid bootstrap server notations

Close #1843

Squashed commit of the following:

commit cc82b373816b76a803d29e4baae18384aa0f8c67
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Thu Aug 20 14:20:35 2020 +0300

    * /control/dns_config: allow all valid bootstrap server notations

    * use dnsproxy v0.31.1

home/home_test.go

@@ -142,7 +142,8 @@ func TestHome(t *testing.T) {
 	assert.Equal(t, http.StatusOK, resp.StatusCode)
 
 	// test DNS over UDP
-	r := upstream.NewResolver("127.0.0.1:5354", 3*time.Second)
+	r, err := upstream.NewResolver("127.0.0.1:5354", 3*time.Second)
+	assert.Nil(t, err)
 	addrs, err := r.LookupIPAddr(context.TODO(), "static.adguard.com")
 	assert.Nil(t, err)
 	haveIP := len(addrs) != 0