This patch aims at deleting the records of the archived instances from
the instance_mappings and request_specs tables in the API database
immediately following their archival from instances to shadow_instances
table. So upon running the 'nova-manage db archive_deleted_rows' command
the records of the archived instances will be automatically removed from
the instance_mappings and request_specs tables as well. A warning has
also been added to fix the issue of 'nova-manage verify_instance'
returning a valid instance mapping even after the instance is deleted.
The patch also adds InstanceMappingList.destory_bulk() and
RequestSpec.destroy_bulk() methods for ease of bulk deletion of records.
Change-Id: I483701a55576c245d091ff086b32081b392f746e
Closes-Bug: #1724621
Closes-Bug: #1678056
32fd58813f