Fix `confirmResize` action status code in V2

In server`s action `confirmResize` status code in @wsgi.response
decorator is set as 202 but this is overridden/ignored by return
statement (return exc.HTTPNoContent()) which return 204 status code.

This is very confusing and we should have expected status code in
@wsgi.response decorator as consistence with other APIs.

NOTE- There is no change in API return status code. API returns the
same 204 return code as previously.

Change-Id: Id8033fb8880306babebc14b319bce5b3b8798774
Closes-Bug: #1368597
VMware: Use vm_mode constants

Address missing changes for the vm_mode type from
commit 8fcd1b2c73dad8e2a7b4d299da270934fd5328cc.

Change-Id: Id03dc089af064969501ee2fc9d965a2028f901e4
Co-authored-by: Gary Kotton <gkotton@vmware.com>
Fix SecurityGroupExists error when booting instances

Make sure we properly handle the case when multiple threads check
and create the default security group, if it hasn't existed yet.
One thread will succeed and others will fail (we have a unique
constraint in db to prevent a race condition), so just handle the
exception to let instance boot proceed.

Steps to reproduce:

1) install OpenStack with Rally using DevStack:

    https://github.com/stackforge/rally/tree/master/contrib/devstack

2) fetch the Rally task:

    http://boris-42.github.io/boot.yaml

3) run it

    rally -v task start boot.yaml

Closes-Bug: #1370782

Change-Id: I414637a31b0b540fefa6c1314be6e973e2d4a178
Retry on closing of luks encrypted volume in case device is busy

We're seeing races in the gate on detach of an encrypted volume where
the device is busy so the detach fails, which causes the delete of the
volume on the cinder side to fail because the volume is still in use and
then Tempest times out waiting for the volume to be deleted.

This simply adds a retry to close the encryption device.  I use
attempts=3 since that's what we use for lvremove.

Closes-Bug: #1374458

Change-Id: Ia0667da7dee247ba8c3338b296244b2a71d1045d
Merge "Retry on closing of luks encrypted volume in case device is busy"
Merge "VMware: Use vm_mode constants"
Merge "Fix `confirmResize` action status code in V2"
Merge "Fix SecurityGroupExists error when booting instances"