Better messaging for missing volume components on host to perform mount

pkg/volume/volume.go

@@ -94,6 +94,18 @@ type Attributes struct {
 type Mounter interface {
 	// Uses Interface to provide the path for Docker binds.
 	Volume
+
+	// CanMount is called immediately prior to Setup to check if
+	// the required components (binaries, etc.) are available on
+	// the underlying node to complete the subsequent SetUp (mount)
+	// operation. If CanMount returns error, the mount operation is
+	// aborted and an event is generated indicating that the node
+	// does not have the required binaries to complete the mount.
+	// If CanMount succeeds, the mount operation continues
+	// normally. The CanMount check can be enabled or disabled
+	// using the experimental-check-mount-binaries binary flag
+	CanMount() error
+
 	// SetUp prepares and mounts/unpacks the volume to a
 	// self-determined directory path. The mount point and its
 	// content should be owned by 'fsGroup' so that it can be