Remove used_limits extension from the V3 API

Remove the used_limits extension from the V3 API because
it shows usage for limits which are no longer going to be displayed
by the limits extension. See https://review.openstack.org/#/c/39872/
The limits are not being displayed there because they are already
available through the quotas extension.

Although the quotas extension currently only displays the quota limit
and not usage, the following proposed changeset adds display
of usage: https://review.openstack.org/#/c/32303/. And this is done
in a way which is much more consistent in terms of naming and interface
than used_limits does.

So we no longer need the used_limits extension

Partially implements blueprint nova-v3-api

Change-Id: I8ec1f300335ca4fc3b86323cc3af6bc1591da7bb
ComputeFilter shouldn't generate a warning for disabled hosts

Disabling a service is a normal operation, so this state should
not be included in the same log statement as a host that fails
the service_is_up() check.

A service which is enabled but not up deserved a warning rather
than debug entry.

By separating out the checks we also avoid the service check on
disabled hosts.

Change-Id: I1a398bc033ebe71f42ac117af7dae39502aceede
Closes-Bug: 1254356
Merge "ComputeFilter shouldn't generate a warning for disabled hosts"
Merge "Remove used_limits extension from the V3 API"
XenAPI: Speedup host_ref cannot change - get it once

The host we run on is fixed - getting this each time from XAPI
is expensive

Change-Id: Ifee9a778f3ed855ef52b001de3fc2ebbd0b972cf
XenAPI: get_info was very expensive

Getting the whole VM record is expensive and slowed down Tempest tests
significantly.  Replaced with getting each required item.

When getting power state, only need that specific value, so reduce the
calls to get_info too.

Change-Id: I93bcef5b692a531aac41518dc29d5d4f46cded65
XenAPI: Tidy calls to get_all_ref_and_rec

get_all_records is more efficient than getting them individually in the
old get_all_ref_and_rec implementation.

Replaced some cases of get_all_records with a faster and more
specific API call.

Change-Id: I4725c3f1fdebdf1737941cb7db69b19afb22df9f
XenAPI: Speedup get_vhd_parent_uuid

In many cases the VDI record has already been retrieved.
Use it rather than expensively getting a new VDI record from XAPI.

Change-Id: I469e2a415c1f1924010f47d3927ca18c45a7b8f8
XenAPI: Use get_VALUE in preference to get_record()['VALUE']

Replaces calls to get_record where only a single item is retrieved
from the record with the specific get_VALUE call.

Change-Id: I52e20c4f4c9d6a6ad019694916ee057cc96b18a6
XenAPI: Synchronize on all VBD plug/unplug per VM

Dynamically adding or removing a device needs to be synchronized
to work around a bug in XenServer 6.1 and 6.2 where simultaneous
events can be partially ignored, leading to a failure to plug or
unplug.

Change I041365ed863a1a1c55e88025dff42d01c35494a2 attempted to
work around the issue by retrying - however that does not catch
all failures.  This change should eliminate some of the known
INTERNAL_ERROR failures, but not all, so I041 should not be
reverted.

Change Ie7a64c481a9e3874df9d5924fbb050ac7ab117db does the same
as this, but only for VBD.plug.

Change-Id: If78d4e5f1dd84f1d4a588f25b8f887a7b125bbea
Closes-bug: 1217972