Better messaging for missing volume components on host to perform mount

pkg/volume/rbd/rbd.go

@@ -381,6 +381,13 @@ func (b *rbd) GetAttributes() volume.Attributes {
 	}
 }
 
+// Checks prior to mount operations to verify that the required components (binaries, etc.)
+// to mount the volume are available on the underlying node.
+// If not, it returns an error
+func (b *rbdMounter) CanMount() error {
+	return nil
+}
+
 func (b *rbdMounter) SetUp(fsGroup *int64) error {
 	return b.SetUpAt(b.GetPath(), fsGroup)
 }