Using common methods from oslo cliutils

There are some common methods in cliutils we can use in novaclient:
 arg, env, unauthenticated, isunauthenticated.

 + Replaces utils.env to add alias env from cliutils.
 + Replaces utils.arg to add alias arg from cliutils.
 + Removes unused methods: add_arg, unauthenticated, isunauthenticated
   To use methods from clituils.

Related to blueprint common-client-library-2
Change-Id: Ic7c132c37d6a91cf3eae55530300efd153c31903
Merge "Using common methods from oslo cliutils"