Fix vbmc role fails on missing virtualenv
Fix vbmc role fails on missing virtualenv

    * Task "check if there's a virtualenv already installed" is failed when
      virtualenv is not installed, added ignoring error for that.

Change-Id: I3b251e1657ea0c9f74c2b804603fa9c28bbf2f1e

redhat-openstack/infrared,redhat-openstack/infrared,redhat-openstack/infrared