[compute] always set instance.host in post_livemigration

This change add a new _post_live_migration_update_host
function that wraps _post_live_migration and just ensures
that if we exit due to an exception instance.host is set
to the destination host.

when we are in _post_live_migration the guest has already
started running on the destination host and we cannot revert.
Sometimes admins or users will hard reboot the instance expecting
that to fix everything when the vm enters the error state after
the failed migrations. Previously this would end up recreating the
instance on the source node leading to possible data corruption if
the instance used shared storage.

Change-Id: Ibc4bc7edf1c8d1e841c72c9188a0a62836e9f153
Partial-Bug: #1628606
(cherry picked from commit 8449b7caefa4a5c0728e11380a088525f15ad6f5)
(cherry picked from commit 643b0c7d35752b214eee19b8d7298a19a8493f6b)
(cherry picked from commit 17ae907569e45cc0f5c7da9511bb668a877b7b2e)
(cherry picked from commit 15502ddedc23e6591ace4e73fa8ce5b18b5644b0)
(cherry picked from commit 43c0e40d288960760a6eaad05cb9670e01ef40d0)
(cherry picked from commit 0ac64bba8b7aba2fb358e00e970e88b32d26ef7e)

0 files changed, 0 insertions, 0 deletions