Make separate calls to libvirt volume

This is a follow up patch to
https://review.openstack.org/#/c/116998/, where libvirt
volume's connect_volume method were split into get_config and
connect_volume. The following patch changes libvirt driver
to call the appropriate volume method, get_config or
connect_volume, instead of the old monolithic call to
connect_volume. connect_volume will no longer need to return
the libvirt xml after this switch over. This will improve
performance and eliminate possible race conditions.

Change-Id: I0d0d7ba98c53ad7509c28bb4866c488c0a049d2f
Closes-Bug: #1359617
Split and fix the type filters unit tests

The unit test for TypeAffinityFilter was broken -- it was passing in the
instance_type['name'] key, when the filter class actually checks the
'id' key of the instance_type property of the filter_properties dict. :(

This corrects the tests, removes all DB accesses from both the type and
aggregate type affinity filter unit tests, and splits them out into
their own test file.

Change-Id: I5fc27c538cc419b4ed972839751e0e779151fc58
Remove warning & change @periodic_task behaviour

During development of Juno, Ia227f4c4e69ecf361ab02d1d17a3010303650104
added a warning that the behaviour of periodic_tasks with an interval of
0 would change.  This patch changes the behaviour and removes the
warning.

Oslo (which provides the @periodic_task decorator) uses spacing=0 to
mean "run at the default interval of 60s", but several nova methods used
spacing=0 to mean "don't run".  These methods now behave consistently
with the Oslo code.

Due to an error in the original patch, some of the warnings refer to the
intended behaviour change as being in "the K release", and some to "Juno".
The warning about changing behaviour is first present in Juno, so this
patch should be merged in Kilo.

Change-Id: Ie5f2092a3b84e3674fe6a68ce511d2dc218bb625
Closes-bug: 1276203
Merge "Remove warning & change @periodic_task behaviour"
Merge "Split and fix the type filters unit tests"
Merge "Make separate calls to libvirt volume"