Sync latest install_venv_common.py
Sync latest install_venv_common.py

Syncs:

c78b2ab Avoid using cfg in install_venv_common

So that people don't need oslo-config installed to run install_venv

Fixes bug 1130853

Change-Id: I9dfc8d8417455ff22a0d0e911c762983952c75ee

takeshineshiro/glance,SUSE-Cloud/glance,ntt-sic/glance,ozamiatin/glance,klmitch/glance,darren-wang/gl,openstack/glance,saeki-masaki/glance,paramite/glance,stevelle/glance,kfwang/Glance-OVA-OVF,ozamiatin/glance,akash1808/glance,vuntz/glance,cloudbau/glance,tanglei528/glance,akash1808/glance,JioCloud/glance,openstack/glance,scripnichenko/glance,rajalokan/glance,openstack/glance,wkoathp/glance,paramite/glance,klmitch/glance,rickerc/glance_audit,SUSE-Cloud/glance,vuntz/glance,sigmavirus24/glance,rickerc/glance_audit,JioCloud/glance,kfwang/Glance-OVA-OVF,redhat-openstack/glance,redhat-openstack/glance,jumpstarter-io/glance,scripnichenko/glance,dims/glance,wkoathp/glance,jumpstarter-io/glance,cloudbau/glance,rajalokan/glance,stevelle/glance,citrix-openstack-build/glance,dims/glance,takeshineshiro/glance,darren-wang/gl,saeki-masaki/glance,ntt-sic/glance,sigmavirus24/glance,citrix-openstack-build/glance,tanglei528/glance