Fix import for install_venv.py

On systems that don't use devstack the nova directory
doesn't automatically get added to the python path. This
breaks tools/install_venv_common.py which imports from
nova.openstack.common. This fixes the issue by manually
adding the nova root directory to the python path before
tools/install_venv_common.py is imported.

Change-Id: I8a3df02a51c2c777d8f47cb8bc72d0644ae47095

tools/install_venv.py

@@ -22,6 +22,9 @@
 import os
 import sys
 
+parentdir = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+os.sys.path.insert(0, parentdir)
+
 import install_venv_common as install_venv