Test wrong IP version of prefix in security rule

Negative tests combines wrong sombination of ethertype and
IP prefix arguments in security rule creating. Shall be BadRequest
response and appropriate error message.

Change-Id: Iefdc45555beb2ff0807925efc7fc992e30f14899
DHCP6 Tests fail to remove DVR ports

The method _clean_network() only removes centralized
router interface ports since it uses only 'network:router_interface'
as a valid router interface port.

Change-Id: Ic647d27c5c4e3bcb8ec0349e31684204e3d0c569
Closes-bug: #1403983
Actually attach a volume to an instance before taking snapshot

In the test test_snapshot_create_with_volume_in_use, the test calls Cinder
"os-attach" for attaching a volume. The "os-attach" to tell Cinder the
volume is attached, but the API doesn't actually attach the volume to an
instance.(Only update volume status in DB)

This is not right test case for taking a snapshot with in-use volume.
In this test, Nova "os-volume_attachment" should be called for volume
attachment.

Also, some Cinder drivers fails assisted snapshot due to this problem.
In order to perform the snapshot properly, this fix is needed.

Closes-Bug #1401110
Change-Id: Ib31e351fe7c3d27824241cf142c213eae287483f
Improve error message on exception raised by get_default

This commit adds a missing message from the InvalidConfiguration
exception raised by the get_default method in the credentials classes.
Without an explanatory message it is very difficult for users to
identify the cause of the configuration error.

Change-Id: I709500fd32bdc86766de4f72e2032591c2f7aaa3
Add VolumeClient for cleanup

In volume clients, there is a lot of duplicated code for
setting CONF. This patch adds VolumeClient for removing them.

Change-Id: I4be9678656d0da5689070959c7f56c2ed903dd69
Merge "Improve error message on exception raised by get_default"
Merge "Test wrong IP version of prefix in security rule"
Merge "Actually attach a volume to an instance before taking snapshot"
Merge "Add VolumeClient for cleanup"
Merge "DHCP6 Tests fail to remove DVR ports"