Ensure deleted instances' status is always DELETED

Currently when deleting failed instances that were never assigned a
host, their vm_state is left in 'error' instead of 'deleted'. This is a
problem when invoking the Index Instances REST API with a Changes-Since
query parameter since that API returns both deleted and non-deleted
instances, but currently the failed deleted instances are incorrectly
marked as status:ERROR instead of status:DELETED.

This patch modifies the server ViewBuilder to ensure the status is
correctly set.

Change-Id: I614714676bab4986564b236d74f2c0d77400e48c
Closes-bug: #1243301
Rename _get_vm_state to _get_vm_status

The method is actually used to get the server's "status", so rename it
to better reflect function.

Change-Id: Ie4b0a1c76c81f6d08250a1cfd594429ef9eaf5ae
Remove unused local variables in test case

Non-functional change. Just remove the variables that had been assigned
but were never used for clarity of the code base.

Change-Id: I4c204067cff161a975df2277d6ef9d2081863bd1
Periodic task _poll_unconfirmed_resizes can now use slave db

This allows the _poll_unconfirmed_resizes periodic task to use the
slave db for reads if the deployment has a slave configured. For
slaveless deployments behavior remains unchanged.

This commit advances the MigrationList object to version 1.1

Change-Id: I10bf729e92dc599819ef74a97a834c7f2df5b162
Partially-implements: blueprint periodic-tasks-to-db-slave
Merge "Ensure deleted instances' status is always DELETED"
Merge "Rename _get_vm_state to _get_vm_status"
Merge "Remove unused local variables in test case"
Merge "Periodic task _poll_unconfirmed_resizes can now use slave db"