Add support for flex volume. Flex volume adds support for thirdparty(vendor)

volumes and custom mounts.

pkg/volume/plugins.go

@@ -59,7 +59,7 @@ type VolumePlugin interface {
 	// Init initializes the plugin.  This will be called exactly once
 	// before any New* calls are made - implementations of plugins may
 	// depend on this.
-	Init(host VolumeHost)
+	Init(host VolumeHost) error
 
 	// Name returns the plugin's name.  Plugins should use namespaced names
 	// such as "example.com/volume".  The "kubernetes.io" namespace is
@@ -263,7 +263,12 @@ func (pm *VolumePluginMgr) InitPlugins(plugins []VolumePlugin, host VolumeHost)
 			allErrs = append(allErrs, fmt.Errorf("volume plugin %q was registered more than once", name))
 			continue
 		}
-		plugin.Init(host)
+		err := plugin.Init(host)
+		if err != nil {
+			glog.Errorf("Failed to load volume plugin %s, error: %s", plugin, err.Error())
+			allErrs = append(allErrs, err)
+			continue
+		}
 		pm.plugins[name] = plugin
 		glog.V(1).Infof("Loaded volume plugin %q", name)
 	}