Currently 'openstack database flavor list' command fails when using
'--datastore-type' and '--datastore-version-id' options. This change
fixes the issue by correcting keyword arguments.
This change also adds a test case of listing flavors with the optional
arguments.
Change-Id: I37be4911d4dda1529e2550344a912e0aa3c50558
Closes-Bug: #1794663
84b1b0ae62