lvm: unhandled exception when migrating volume

Catches the StopIteration exception if the destination volume group
does not exist when attempting to migrate a volume.

Change-Id: I0b5dd15e4c7198fe54abf1aa917a60554adcd568
Closes-Bug:  #1277512
Fix cinder-backup volume restore with ceph driver

Restore operations currently break if restoring to
the backup source volume, that volume is an rbd and
the associated backup was incremental.

Change-Id: Ieafe6ab2d1a15cad2b534a3aab0df29eb8591306
Closes-Bug: 1276977
Remove unused exception

 o class WillNotSchedule(CinderException):

   This exception was removed in the following commit.

    commit cea7fe21cecfcd28ede3ba411b8ab8b36c9a7c15
    Author: Zhiteng Huang <zhithuang@ebaysf.com>
    Date:   Thu Jan 2 15:44:30 2014 +0800

        Drop Chance/SimpleScheduler Implementation

Change-Id: I8f5f8e6c5c844a67607dae9fb63524aef7069133
Merge "Fix cinder-backup volume restore with ceph driver"
Merge "lvm: unhandled exception when migrating volume"
Merge "Remove unused exception"