Remove race condition (in FloatingIps)

Soft delete all duplicate rows with the same address except one with
the biggest value in `id` column.

Create UC on columns (address, deleted)

Fix floating_ip_create
  Replace Select then Insert -> Try to Insert.

Fix floating_ip_bulk_create
  Replace get all and locally compare -> Try to Insert

Fix floating_ip_update
  If we update floating_ip with existing address, raise
  rollback and raise FloatingIpExists

Add missing test for floating_ip_update to duplicate

Fixes bug 1145216

blueprint db-enforce-unique-keys

Change-Id: Idd0c8305ca348700235f757a29fc7998edca576b
Merge "Remove race condition (in FloatingIps)"