Currently the nova-manage delete_cell command with the --force option
allows us to destroy hosts_mappings of the cell which does not have any
instances or instance_mappings. This patch extends this command with the
--force option for destroying instance_mappings in addition to the
host_mappings of the cell which is to be deleted. Note that the instance
mappings and host mappings are only removed if there are no living
instances in the cell. So a --force delete here will not work if there
are non-deleted instances.
Change-Id: Ibefa0465224bec9a22431c7d3b5c8f5d91fc7732
Closes-Bug: #1745375
ee2f65d91f