Compact pre-Icehouse database migrations <= 140.

Compacts the pre-Icehouse database migrations <= 140 into a single
migration (140_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 counters to bw_usage_cache table.

2) Add node to instances.

3) Add indexes to instances.

4) Add indexes to migrations.

5) drop server name from instances
 NOTE: for sqlite this change recreated the instances table altogether.

6) add indexes to fixed ips.

7) Drop unused postgresql volume sequences.

Change-Id: I0405c02191a47b96759131bf6b7a1379f4b5711e
Implements: blueprint compact-havana-db-migrations
Merge "Compact pre-Icehouse database migrations <= 140."