Compact pre-Icehouse database migrations <= 160.

Compacts the pre-Icehouse database migrations <= 160 into a
single migration (160_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) Make task_log period_begining, period_ending a DateTime.

 2) Change type of deleted column.

 3) Create shadow tables.

 4) Add task log unique constraint.

 5) Add security_group_default_rules table.

 6) Add networks unique constraint.

 7) Revert ip column length.

NOTE: This patch removes the 184_sqlite_upgrade.sql and
184_sqlite_downgrade.sql migrations since these were causing
new test failures and the standard DB migration seems to take
care of it.

Implements: blueprint compact-havana-db-migrations

Change-Id: If977e5f02fffbfb1bc257b3beddf2d7133e6c7b9
Merge "Compact pre-Icehouse database migrations <= 160."