Use error instead of warning to log mount exc

Gluster's driver uses warning to log mount exceptions. This patch
replaces that warning with an error message.

Change-Id: I54a10ec8abf460ca9ff7bb009b8d702cfad0fed0
Closes-Bug: #1317573
Ensure metadata is saved before updating volume status

This patch ensures the volume metadata is saved to
the snapshot metadata before updating the status
of the snapshot to be available.

Change-Id: Iada010520dc3c086fcd410a6c7fd152cf4a31561
Closes-Bug: #1310991
Merge "Ensure metadata is saved before updating volume status"
Merge "Use error instead of warning to log mount exc"