Prevent clean-up of migrating instances on compute init

During compute manager startup init_host is called. One
of the functions this carries out is to delete instance
data that doesn't belong to this host this function only
checks if the local instance belongs to the host or not.
It doesn't check the task_state. This could result in the
loss of all instance data if it occured at the wrong
point during live migration.

This change checks if the task_state of the instance to
be deleted is MIGRATING and if so it does not delete the
instance. Similarily for the task state RESIZE_MIGRATING.

This change adjust little about the unit test according to
actual code path in icehouse.
Conflicts:
	nova/tests/compute/test_compute_mgr.py

Change-Id: Ia8c67acf93d71af868907f0711dcc1dfe103560c
Closes-Bug: 1319797
(cherry picked from commit 340cae5466eaf5568c4f0eecb2a2fa7cdbcc0ba4)
Merge "Prevent clean-up of migrating instances on compute init" into stable/icehouse