Fixed columns list in indexes.

Migration 152 changed the type of `deleted` column from Boolean to
table.id.type for all tables. Also (as side effect) this migration
removed column `deleted` from indexes (in MySQL) or removed whole
indexes (in PostgreSQL). Current migration fixes these indexes.

Fixes bug 1191724

Change-Id: I3d95d102f379c3817bb372fefb1b12cf5de8a4db
Add unique constraint to FixedIp.

Added unique constraint `uniq_fixed_ips0address0deleted` ('address',
'deleted') to FixedIp model and migrate sripts.
Added new exception `FixedIpExists`. Updated functions `fixed_ip_create`
and `fixed_ip_bulk_create`.
Tests updated respectively.

blueprint db-enforce-unique-keys

Change-Id: I34d0d0dd84e66f325f81fc8223fbf261b22e8d1e
Merge "Fixed columns list in indexes."
Merge "Add unique constraint to FixedIp."