Detach volumes when unavailable

This patch makes sure we detach a volume if is unavailable before
raising a DeviceUnavailable exception.

HISTORY.rst

@@ -5,6 +5,10 @@ History
 0.2.3 (2018-MM-DD)
 ------------------
 
+- Bug fixes:
+
+  - Detach a volume when it's unavailable.
+
 - Features:
 
   - Provide better message when device is not available.

cinderlib/objects.py

@@ -726,6 +726,7 @@ class Connection(Object, LazyVolumeAttr):
             LOG.exception(error_msg)
 
         if error_msg:
+            self.detach(force=True, ignore_errors=True)
             raise cinder_exception.DeviceUnavailable(
                 path=self.path, attach_info=self._ovo.connection_information,
                 reason=error_msg)