Support nova service-disable/enable for Hypervisor

To prevent further scheduling of instance launch on a compute we
need to run:

* nova service-disable --reason REASON NODENAME nova-compute

It would be helpful if we can send this through the hypervisors menu.
New Actions: 'Disable Service' and 'Enable Service' will be added to
Admin -> Hypervisors -> Compute Host action menu to disable/enable
service. So this is a small but useful addition to horizon.

Implement blueprint: service-disable-enable

Change-Id: Ic58d6a6410ec640aecd808ef3e586026e562ac6a
Gracefully handle failures to retrieve a flavor

In some cases, a flavor in use can become unaccessible, for instance
after deleting a flavor with access restrictions.

 * On the Instance details page, make the try/except blocks for API
   calls more fine-grained. Some specific failures shouldn't cause the
   whole page to fail to load (and e.g. prevent Console access).

 * Fix the Resize Instance form to display even if information about
   the current flavor cannot be retrieved.

 * Gracefully handle failures to retrieve flavor information on AJAX
   calls for row update, so that the row doesn't disappear from the
   table.

Change-Id: I011b6e01eca3e04e5ef2528732b9bde3782b4eba
Closes-Bug: #1366166
Imported Translations from Transifex

For more information about this automatic import see:
https://wiki.openstack.org/wiki/Translations/Infrastructure

Change-Id: I4c26755007df27ed5f4c3993bdee5e11890e7604
Merge "Support nova service-disable/enable for Hypervisor"
Merge "Gracefully handle failures to retrieve a flavor"