RHEV: vdsm fails to start with permission denied error on libvirt socket

Issue

• VDSM fails
• host unable to install
• host not reachable
• following error can be seen while (re)starting vdsm:

  File "/usr/lib/python2.6/site-packages/vdsm/libvirtconnection.py", line 151, in get
    conn = _open_qemu_connection()
  File "/usr/lib/python2.6/site-packages/vdsm/libvirtconnection.py", line 95, in _open_qemu_connection
    return utils.retry(libvirtOpen, timeout=10, sleep=0.2)
  File "/usr/lib/python2.6/site-packages/vdsm/utils.py", line 1087, in retry
    return func()
  File "/usr/lib64/python2.6/site-packages/libvirt.py", line 102, in openAuth
    if ret is None:raise libvirtError('virConnectOpenAuth() failed')
libvirtError: Failed to connect socket to '/var/run/libvirt/libvirt-sock': Permission denied
clientIFinit::DEBUG::2015-12-03 10:54:51,483::libvirtconnection::150::root::(get) trying to connect libvirt