we should not encode in base64 the string directly 'string'.encode('base64')

[Chmouel Boudjnah]

Since 'string'.encode('base64') is not supported in python3 let use the standard base64 module instead.

This is the kind of python3 error we are getting currently :

======================================================================
FAIL: novaclient.tests.v1_1.test_servers.ServersTest.test_create_server_userdata_unicode
tags: worker-3
----------------------------------------------------------------------
Empty attachments:
  stderr
  stdout

Traceback (most recent call last):
  File "/Users/GIT/openstack/python-novaclient/novaclient/tests/v1_1/test_servers.py", line 120, in test_create_server_userdata_unicode
    '/tmp/foo.txt': six.StringIO('data'), # a stream
  File "/Users/GIT/openstack/python-novaclient/novaclient/v1_1/servers.py", line 658, in create
    **boot_kwargs)
  File "/Users/GIT/openstack/python-novaclient/novaclient/base.py", line 363, in _boot
    'contents': data.encode('base64'),
LookupError: unknown encoding: base64

[Chmouel Boudjnah (chmouel)]

Never mind this is already fixed in 1229161