Fix removal of storage directory on shared file storage

This patch makes _RemoveDisks symmetric to _CreateDisks with respect
to file-based storage: _CreateDisks uses "in constants.DTS_FILEBASED",
whereas _RemoveDisks was not update and only uses "==
constants.DT_FILE". This results in stale directories left on the
filesystem.

Fixes issue 262.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

lib/cmdlib.py

@@ -9038,7 +9038,7 @@ def _RemoveDisks(lu, instance, target_node=None, ignore_failures=False):
     for port in ports_to_release:
       lu.cfg.AddTcpUdpPort(port)
-  if instance.disk_template == constants.DT_FILE:
+  if instance.disk_template in constants.DTS_FILEBASED:
     file_storage_dir = os.path.dirname(instance.disks[0].logical_id[1])
     if target_node:
       tgt = target_node