Allow virtual-kubelet to use cluster domain

This allows `--cluster-domain` to be passed to virtual kubelet like a
traditional kublet, and use this to generate search-domains for
`/etc/resolv.conf`

* Set default `cluster-domain` to `cluster-local` to match current kubelet

Related: #641

Signed-off-by: Graham Hayes <gr@ham.ie>

providers/store.go

@@ -62,12 +62,13 @@ func (s *Store) Exists(name string) bool {
 
 // InitConfig is the config passed to initialize a registered provider.
 type InitConfig struct {
-	ConfigPath      string
-	NodeName        string
-	OperatingSystem string
-	InternalIP      string
-	DaemonPort      int32
-	ResourceManager *manager.ResourceManager
+	ConfigPath        string
+	NodeName          string
+	OperatingSystem   string
+	InternalIP        string
+	DaemonPort        int32
+	KubeClusterDomain string
+	ResourceManager   *manager.ResourceManager
 }
 
 type InitFunc func(InitConfig) (Provider, error)