Compact pre-Icehouse database migrations <= 180.

Compacts the pre-Icehouse database migrations <= 180 into a
single migration (180_havana.py).

Pre-Icehouse users will now need to upgrade to Havana before
running any Icehouse migrations.

Tested on MySQL and PostgreSQL schemas on Fedora 19 to ensure the
new compacted migration generates an identical schema to the
previous migrate scripts in Havana.

Specific changes include:

 1) Add uniq_name_x_deleted, uniq_flavorid_x_deleted constraints.

 2) Add key_pairs_uniq_name_and_user_id constraint.

 3) Add uniq_instance_type_id_x_project_id_x_deleted constraint.

 4) Add uniq_address_x_deleted constraint (floating ips)

 5) Add availability_zone to volume_usage_cache.

 6) Add compute node stats index.

 7) Change cells deleted to int (except for shadow table
   which is handled in 181_fix_179_migration_sync_shadow_table)

Change-Id: I09fdb1a2e509a3d828b83b78d38a484fe405558b
Implements: blueprint compact-havana-db-migrations
Merge "Compact pre-Icehouse database migrations <= 180."