nova should depend on openstackx and load appropriate osapi_extensions by default

[Adam Gandelman]

If we wish to support the Horizon dashboard out-of-the-box, it is necessary for nova-api to depend on the openstackx python libary [1] to provide necessary middleware.

With the appropriate dependencies installed, we would also need to add configuration flags to nova.conf in order to load these extensions, similar to:

--osapi_extension=extensions.admin.Admin
--osapi_extension=nova.api.openstack.v2.contrib.standard_extensions

These options can be activated outside of packaging via Juju charms, but I predict many people will expect dashboard and the middleware it depends on to be functional out-of-the-box, like other openstack components (especially for one-node installs)

Related note: Bug #906649 needs to be resolved in order for any of this to be functional.

[1] Or at least until openstackx is deprecated entirely in favor of python-novaclient, I'm not sure when this is due to happen. For now, its still required.

[Adam Gandelman (gandelman-a)]

Note: This will likely be marked invalid soon, as the openstackx library is soon to be marked deprecated and removed in favor of python-novaclient.

Another note: the osapi_extensions flag has been renamed to osapi_compute_extensions.

[Adam Gandelman (gandelman-a)]

openstackx has been removed as a dependency