Fix availability zone client in compute admin test

In /tempest/api/compute/admin/test_availability_zone.py file,
V3 test class use the V2 Availability Zone client.

This patch correct the client for V2 and V3 by instantiating the
correct one in base class.

Change-Id: I97903b1ea7faa02c5880c091a166e386295de0da
Remove docutils pin

This was added to work around bug 1091333.  A new sphinx has been
released and so this is no longer necessary.

Change-Id: I6ea61a3cc441dd1ca2ced7e2fd837a55b917f76d
Always pass str to shlex.split for py26 compat

On python 2.6 shlex.split cannot handle unicode,
which can lead to TypeError exception.

Details can be seen in
http://bugs.python.org/issue6988
and
http://bugs.python.org/issue1548891

As best solution it seems to decode *cmd* to utf-8 str
before passing to shlex.split().

Change-Id: If56a6f16ab712691b26035d0cd3d7d70260a64c6
Merge "Remove docutils pin"
Merge "Always pass str to shlex.split for py26 compat"
Merge "Fix availability zone client in compute admin test"