Add check for BlockDeviceMappingV2 nova extension

Booting instance from image (creates a volume) option is using
the new BDM format when submitting the create server request to
Nova. Adding a check for Nova extensions if it is supported
before displaying the option.

Closes-bug: #1223875

In the original fix API call is not wrapped with try/except
and it was fixed in bug 1262223 in master. The fix is also
cherry-picked from commit a10436e6a376fb2c3478796e7ad728eb0e1f0ba3.

Related-bug: #1262223

Change-Id: Ie0b2b5d574babc910e2dac7ce9e3ab6603382ffb
(cherry picked from commit a10436e6a376fb2c3478796e7ad728eb0e1f0ba3)
Merge branch 'stable/havana' of https://github.com/openstack/horizon into stable/havana_routerrules