LVM: Volume is deleted unexpectedly during volume migration

When using LVMISCSIDriver, a volume is unexpectedly deleted during
volume migration operation. This problem only occurs when the
volume_group of backend A and backend B is same value such as
misconfiguration. Even if the configuration is wrong, cinder should
not delete the volume unexpectedly for user.

Closes-Bug: 1404013
Change-Id: I010be0c70589459a488cdef7cd83380eab27c61c
Mock leaked _execute() calls in driver tests

Some drivers have _execute() calls being linked, causing tests to prompt
for password and eventual fail for time out. This prevents those
_execute calls from happening.

Closes-Bug: #1404414
Change-Id: I43a11c065799efe6f5b81dc15e1f7232c80d1070
Merge "Mock leaked _execute() calls in driver tests"
Merge "LVM: Volume is deleted unexpectedly during volume migration"