Optimize db.instance_floating_address_get_all
Was:
Get FixedIps with corresponding instance_uuid
For each FixedIp get associated FloatIp (N request)
Now:
Get only list of FixedIps ids
Get all corresponding FloatingIp with one query (select in)
Get only addresses from FloatingIps (because we are using only it)
Add temporary test for db.instance_floating_address_get_all to
ensure that it works as expected.
Change-Id: Id3c515de0ca35707bbfe46b991c2d7cf591e431b