Set install_requires in setup.py.
Set install_requires in setup.py.

Updates setup.py to set install_requires using parse_requirements from
openstack-common.  This allows DevStack to install nova requirements, as
currently they are not handled.

Also relaxes the version requirement for lxml to >=2.3,<3.  This allows
DevStack to install nova requirements without needing to install lxml
over the installed python-xml system package, currently 2.3.2.

Change-Id: Iccebf9604ba5c6fcacb4c5fa5004f9fcb08944f3

n0ano/ganttclient