Allow name argument to flavor-access-add

Administrator cannot use the flavor name in arguments of
"nova flavor-access-add" and "nova flavor-access-remove"
in following conditions.

1. The flavor is non-public.
2. The falvor doesn't belong administrator's tenant.

This patch fixes this problem.

Change-Id: Ic5e3222d0ff62667e003a61e6a94e85833da5d11
Fixes: bug #1205298
Merge "Allow name argument to flavor-access-add"