Remove attempts to reinstall python-keystoneclient from Keystone cookbook into Nova venv

the current Nova requires next version of keystoneclient

Traceback (most recent call last):
  File "/opt/nova/.venv/bin/nova-api", line 4, in <module>
    from pkg_resources import require; require('nova==2013.1.4.a20.g43f2a4c')
  File "/opt/nova/.venv/local/lib/python2.7/site-packages/distribute-0.6.24-py2.7.egg/pkg_resources.py", line 2711, in <module>
    parse_requirements(__requires__), Environment()
  File "/opt/nova/.venv/local/lib/python2.7/site-packages/distribute-0.6.24-py2.7.egg/pkg_resources.py", line 588, in resolve
    raise VersionConflict(dist,req) # XXX put more info here
pkg_resources.VersionConflict: (python-keystoneclient 0.2.5 (/opt/nova/.venv/lib/python2.7/site-packages), Requirement.parse('python-keystoneclient>=0.3.0'))