Change RPC post_live_migration_at_destination from call to cast

We don't expect post_live_migration_at_destination to return anything,
so change call to cast.

Change-Id: Iccdb6e195d1d5d9b96e1372206823d414caae872
nova docker driver cannot find cgroup in /proc/mounts on RHEL

In order to support the docker hypervisor on rhel/centos or fedora
we had to adapt the function which resolves the cgroup path.

Change-Id: Ie24028f822d91d65d4f90a7941e7b11874a3b425
Closes-Bug: #1243101
libvirt: Fix confusing use of mox.StubOutWithMock

The code was using a side effect of mox.StubOutWithMock to reset
libvirt_driver.LibvirtDriver._conn after a test before resetting it manually.
This code is shorter, and it's obvious what it does.

Change-Id: I78393f76e132397dd198ac4b6ff998c785ff5690
Merge "libvirt: Fix confusing use of mox.StubOutWithMock"
Merge "Change RPC post_live_migration_at_destination from call to cast"
Merge "nova docker driver cannot find cgroup in /proc/mounts on RHEL"