Add validation of available_zone during instance create

When using nova boot command with --availability_zone parameter and only
input the zone without host and node, now will check if the zone is
available, if not, then return an error message directly rather than
create an instance with an Error state

Add a get_only_available option to function get_availability_zones

To disable available zone, one should have to disable both the scheduler
filter and the API extension, if the API extension is not disabled, this
patch will still do the validation of available zone

DocImpact

Change-Id: Ibff117d48b60ac4f4ae33e3b3d2840d7313ce0d4
Merge "Add validation of available_zone during instance create"