cleanup: move core functions to core pkg

as we are refractoring the cephfs code,
Moving all the core functions to a new folder
/pkg called core. This will make things easier
to implement. For now onwards all the core
functionalities will be added to the core
package.

Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>

internal/cephfs/errors/errors.go

@@ -62,3 +62,9 @@ var (
 	// ErrVolumeHasSnapshots is returned when a subvolume has snapshots.
 	ErrVolumeHasSnapshots = coreError.New("volume has snapshots")
 )
+
+// IsCloneRetryError returns true if the clone error is pending,in-progress
+// error.
+func IsCloneRetryError(err error) bool {
+	return coreError.Is(err, ErrCloneInProgress) || coreError.Is(err, ErrClonePending)
+}