novaclient sort parameters support

Adds sorting support to the 'nova list' command.

--sort <key>[:<direction>]

The --sort parameter is comma-separated and is used to specify
one or more sort keys and directions. The direction defaults to
'desc' for each sort key and the user can supply 'asc' to
override.

Partially implements: blueprint nova-pagination

Change-Id: I635e017c7f9ab61812333983bfecccd6fce8d394
Merge "novaclient sort parameters support"