Network: ensure that ports are 'unset' when instance is deleted

Commit a141206e9dfd31955b9b31d9e5a7f73bbd8510ca ensured that user defined
ports were not deleted when an instance is deleted or rescheduled. The
problem with this commit is that it did not reset the 'device_id' and
'device_owner' of the port. This leads to port leakage and eventually a tenant
is unable to launch any instances as their port quota has exceeded the
allocated amount.

The solution is for the deallocation to reset the 'device_id' and the
'device_owner' of the port. This is allocated when the port is actually assigned
to an instance.

In the case of minesweeper (which runs on OpenStack), the tenant was leaking ports.
The root cause was that the user defined ports were assigned to a specific instance,
which was deleted, as a result of a failed reschedule (which is legitimate).

When an instance is deleted all artificats of that instance should be reset on the
port.

Change-Id: Ie1516c299ce6d79faf2d5103a14d6d8931d3ede2
Closes-bug: #1321381
Check the network_info obj type before invoke wait function

When instance schedule to host and it isn't first time schedule,
the instance may already allocated network. And then the code
will return an NetworkInfo object, not an NetworkInfoAsyncWrapper.
The checking code only assume it is NetworkInfoAsyncWrapper object.

Change-Id: I987902fc47e509e4fd08f762d66b16c09eaf5008
Partial-Bug: #1326207
Sync "Prevent races in opportunistic db test cases"

This sync change Id82090743e8b93f6c960de066fd05d8a2f9fb934 from
oslo-incubator

Opportunistic db test cases create schemas on demand, so that each
test case which inherits the base test case class, will get its own
db schema (i. e. races between tests are not possible).

In order to do schema provisioning we have to connect to RDBMS server
first. So far we've been connecting to the openstack_citest database,
which is guaranteed to exist on CI nodes. It turns out, there are a
few test cases in Nova (maybe in other projects as well), that drop
and recreate the openstack_citest database. If they happen to do that
when the opportunistic db fixture is in the middle of provisioning a
schema, those tests will fail (as there is an open session to the
database and thus it can't be dropped).

This can be solved easily by changing the way we provision new
schemas in opportunistic db test cases as actually, we don't have to
connect to the openstack_citest database at all:

 - for MySQL we can use an empty db name to connect to MySQL server,
   but not to a particular database
 - PostgreSQL requires us to specify the database name. We can use
   the service postgres database here (PostgreSQL shell utils such
   as createdb, createuser, etc use it for the very same reason)

Partial-Bug: #1328997

Change-Id: Idc62b24b6ae51ea14f10e39d7b14115e36069637
Merge "Network: ensure that ports are 'unset' when instance is deleted"
Merge "Sync "Prevent races in opportunistic db test cases""
Merge "Check the network_info obj type before invoke wait function"