Add token create subcommand for identity v2 api

Implements token create subcommand which is an equivalent of keystone
token-get command. Original "wrap" parameter for keystone token-get is
not implemented yet due to cliff Bug #1269299

This is a part of: blueprint add-identity-token-support

Change-Id: I9e4de93306f2f5959717b5219621da03961524d8
Merge "Add token create subcommand for identity v2 api"