Cleanup some flavor commands

Some cleanups include:
 - Add flavor sub-commands into README.rst
 - Check flavor ID when creating a flavor
 - Remove check_uuid_like() because it isn't used
 - Remove parameter cs in some _print_XXX functions because cs is
   not used

Change-Id: If47ce557d33db05f53e382f0670f436e05a340b7
Signed-off-by: Shane Wang <shane.wang@intel.com>
Merge "Cleanup some flavor commands"