Unset Hostname when NetworkMode is container

The hostname can not be set on containers using a container network stack

pkg/container/container.go

@@ -138,6 +138,7 @@ func (c Container) StopSignal() string {
 // the options overridden at runtime.
 func (c Container) runtimeConfig() *dockercontainer.Config {
 	config := c.containerInfo.Config
+	hostConfig := c.containerInfo.HostConfig
 	imageConfig := c.imageInfo.Config
 
 	if config.WorkingDir == imageConfig.WorkingDir {
@@ -148,6 +149,10 @@ func (c Container) runtimeConfig() *dockercontainer.Config {
 		config.User = ""
 	}
 
+	if hostConfig.NetworkMode.IsContainer() {
+		config.Hostname = ""
+	}
+
 	if util.SliceEqual(config.Cmd, imageConfig.Cmd) {
 		config.Cmd = nil
 	}