Using common methods from oslo cliutils

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

+ Replaces utils.env to add alias env from cliutils.
+ Removes unused methods in utils: env
To use methods from clituils.

partially implements blueprint common-client-library-2

Change-Id: I295cc80635ed15c91e2832acb315e9deede09516
Merge "Using common methods from oslo cliutils"