Replace basestring by six.string_types

Method shell._boot uses class basestring instead of six.string_types.
Tests don't check this method with several hints, so we didn't have
NameError in py33 env.

Change-Id: I9b35cd7ba162140a15929f9fc8a6d21755b3570c
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
Updates nova client to use the latest oslo files

This patchset updates modules based on the config file:
openstack-common.conf

Notes: Some corrections has been added to work with
new files.
  + utils.py: The method safe_decode from strutils.py
    was updated and it is now not necessary to check for
    decode string with py33.
  + base.py: base64 needs a 8-bit string for py33
  + test_shell.py: stdin.encoding is needed for strutils

Change-Id: Iebe474f1226f8b5faa7fb5722e65f41b80d1973c
Related to blueprint common-client-library-2
Closes-Bug: #1265473
Merge "Replace basestring by six.string_types"
Merge "Updates nova client to use the latest oslo files"
Merge "Using common methods from oslo cliutils"