Fix import log_handler error with publish_errors set

Sync latest module log_handler from Oslo.
Commit Id is 2843a92a0e4007f50d5ad63d51fe574e1ba5e280

This handler sends the error to configured notifier.
The notifier could be any kind (log, RPC, no_op, None).

Note: when using publish_errors you also need to set the
notification_driver option too.

Closes-bug: #1240349
Change-Id: I4f759b049b8f34904ba11382a2e8fc1578677a8f
Remove unused exceptions

The following exceptions are not used.
  class MigrationNotFound(NotFound):
  class BadDriverResponseStatus(VolumeDriverException):
  class InstanceNotFound(NotFound):
  class VolumeRetypeFailed(CinderException):
  class DuplicateSolidFireVolumeNames(SolidFireDriverException):

Change-Id: I891360f9c150eb8ea3f3968f12b9ad3da998981a
Convert RBD unit tests to use mock instead of mox

Change-Id: If32e14a8f5ff180b6c0ff46797bcb81b21f805f1
Closes-bug: 1261864
Storwize driver cleanup

1. Moved Storwize driver into 'ibm' directory and refactored into
   separate files to improve readability and debug-ability. Other IBM
   drivers will be moved into this directory in a separate patch.
2. Errors coming from storage now raise VolumeBackendAPIException,
   and those coming from the driver raise VolumeDriverException.
3. Fixed many pylint errors.
4. Removed any usage of mox from unit tests in favor of mock.

DocImpact

Change-Id: I1696a97279efe834a96b3f3843bc65f0ea6da9cc
GlusterFS: Fix deadlock in volume clone

The create_cloned_volume path could deadlock due to
create_cloned_volume and create/delete_snapshot using the same
lock for synchronization.

Refactor the calls to create/delete snapshot to call the inner
method which does not use a lock.

Introduced by "06999f6 GlusterFS: Synchronize additional op..."

Related-Bug: 1267983
Closes-Bug: 1272092

Change-Id: I84ca34b201c10644faa047f1c9274c14bcdd0359
Updated error messages for volume clone

Updated error messages for volume clone from image,
snapshot and volume to be consistent across.
Updated error messages to indicate the unit (GB).

Change-Id: I9f51ad0c9ce40864a838fca06583d7d4283e61d8
Closes-Bug: #1244609
Merge "Updated error messages for volume clone"
Redundant check in os-migrate_volume_completion

Remove the redundant check for 'migrate_volume_completion', and add the UT
for it.

Change-Id: I6b643dbf9ae1302cafe6748a361123d7d76c437f
Closes-Bug: #1254963
Merge "Fix import log_handler error with publish_errors set"
Merge "Convert RBD unit tests to use mock instead of mox"
Merge "Storwize driver cleanup"
Merge "Redundant check in os-migrate_volume_completion"
Merge "GlusterFS: Fix deadlock in volume clone"
Merge "Remove unused exceptions"