Improve cinder revert-to-snapshot notifications
Improve cinder revert-to-snapshot notifications

The reverting were sending 'revert.end' message without a
corresponding 'revert.start' notification if creating backup
snapshot failed by an exception, so this patch fixes that.

Closes-Bug:#1729793

Change-Id: I2e7acb3f407dab2a8c82191e13d491cdc71d279c
Signed-off-by: Xiaojun Liao <2e8c1e951f00b7420bde37b279619caed0f6747b@gmail.com>

mahak/cinder,openstack/cinder,phenoxim/cinder,j-griffith/cinder,j-griffith/cinder,Datera/cinder,Datera/cinder,phenoxim/cinder,mahak/cinder,openstack/cinder