enable UNMAP when LUN is thin provisioned

- support Block Limits VPD page (0xB0)
 - add UNMAP to REPORT SUPPORTED OPERATION CODES
 - READ CAPACITY(16): set LBPME when Thin provisioning is enabled
 - move Thinprovisioning and BlockShift to config
 - add Unmap to BackingStore

pkg/scsi/backingstore/cephstore_linux.go

@@ -149,3 +149,7 @@ func (bs *CephBackingStore) DataSync() error {
 func (bs *CephBackingStore) DataAdvise(offset, length int64, advise uint32) error {
 	return nil
 }
+
+func (bs *CephBackingStore) Unmap() error {
+	return nil
+}