Re-revert "libvirt: add version cap tied to gate CI testing"

In the following commit the 'version_cap' concept was
reverted in driver.py:

  commit 5dea55785a52b7edb383cf61fab2f65f2ae79a72
  Author: Sean Dague <sean@dague.net>
  Date:   Wed Jul 30 18:57:34 2014 +0000

    Revert "libvirt: add version cap tied to gate CI testing"

Unfortunately, due to a rebase error, when the version checking
code was moved into host.py, the version_cap was re-introduced:

  commit 069ad9a5b4b2cc9b49b21b09b0667909886961cf
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Fri Jul 4 15:12:38 2014 +0100

    libvirt: introduce new 'Host' class to manage the connection

This change reverts it once more

Change-Id: Icf4b2fff1c87d006c9827e5d27b1124e24255c0a
Bump major version of Scheduler RPC API to 4.0

Since Juno, the below deprecated methods were removed from the RPC client:
 - schedule_run_instance
 - prep_resize

Now that we're in Kilo, we only need to care about changes in between 3.0 and
4.0, and there is only one backwards compatibility to leave about flavors.

NOTE : instance_uuids can now be removed from request_spec but it will be
done in a separate commit.

Partially-Implements blueprint request-spec-object

Change-Id: I42d85407f5a98c22607536446f2defec6a994cbc
Remove duplicated constant DISK_TYPE_THIN

Change-Id: Id6d3501e3c8b8cbd392fb533bcfcae288224dcc4
Merge "Re-revert "libvirt: add version cap tied to gate CI testing""
Merge "Remove duplicated constant DISK_TYPE_THIN"
Merge "Bump major version of Scheduler RPC API to 4.0"
first set of changes for scalable schedular
Added Filters for subscription based on type during service startup
1) Initialized self.rpcserver_flavor as dictionary 2) Commented some pdb's 3) Debugs to info 4) Recalculate and subscribe after launching an instance
Added refresh subscribe/unsubscibe for terminate instance
calling update_available_resource to update data before validation. Also needs to add validation if rpc object already present no need to create again
validating rpc object if it is already present for flavor type
modified update resource info call to right location
Fixed invalid iterative rpc server start
resubscribes before as and when resource is allocated(claimed) while launching and resubscribes after deletion of vm is complete
1. In conductor, modified conditional statement (bypass) to the intial stage.
   Need to remove certain schedular related filter code.
2. In compute, modified the queue creation logic, so that queues objects are not
   created multiple times.
   Also added wait() condition, to make sure queue is flushed everytime.
   Identified an issue with oslo.messaging, so addding that repo as well with
   the change - schedular1 branch
Added cpu,ram and disk allocation ratio code. Need to optimize and put them in right location.
Might need to fix code in resource tracker. Basically make them aware about allocation ratio so they don't show wrong values in the log
Removed "scheduler_utils.populate_retry" and added the new code to retry.
We need to identify if retry property at the compute is optional
Missed out changes while rebasing - resource_tracker
Removed pudb