configurable dns search domains

Add a --dns-search parameter and a DnsSearch
configuration field for specifying dns search
domains.

Docker-DCO-1.1-Signed-off-by: Daniel Norberg <daniel.norberg@gmail.com> (github: danielnorberg)

daemonconfig/config.go

@@ -18,6 +18,7 @@ type Config struct {
 	Root                        string
 	AutoRestart                 bool
 	Dns                         []string
+	DnsSearch                   []string
 	EnableIptables              bool
 	EnableIpForward             bool
 	DefaultIp                   net.IP
@@ -49,6 +50,9 @@ func ConfigFromJob(job *engine.Job) *Config {
 	if dns := job.GetenvList("Dns"); dns != nil {
 		config.Dns = dns
 	}
+	if dnsSearch := job.GetenvList("DnsSearch"); dnsSearch != nil {
+		config.DnsSearch = dnsSearch
+	}
 	if mtu := job.GetenvInt("Mtu"); mtu != 0 {
 		config.Mtu = mtu
 	} else {