rm: un-pin python-novaclient

with upgrade of pyrax of 1.9.5, this issue was
resolved.

Change-Id: I7bef7d8795c923bb3c67c2aeeffb97f5a946ac05

tox.ini

@@ -17,8 +17,7 @@ setenv = VIRTUAL_ENV={envdir}
          PYTHONDONTWRITEBYTECODE=1
 deps = -r{toxinidir}/requirements/requirements.txt
        -r{toxinidir}/tests/test-requirements.txt
-commands = pip install python-novaclient==2.26.0
-           pip install -U mock==1.0.1
+commands = pip install -U mock==1.0.1
            pip install git+https://github.com/stackforge/opencafe.git#egg=cafe
            nosetests {posargs:--exclude=api --exclude=endtoend --nologcapture}