bugfix: Graceful shutdown of VM

bugfix: Graceful shutdown of VM

Cleanup phase of PVVP scenario sometimes causes server reboot.
Following updates were made to prevent reboots:
* sleep after VM OS shutdown allows QEMU to finish its own shutdown
procedure
* shared dir was mounted as read only to prevent its modification,
which sometimes causes delays during shutdown; Also warning messages
are causing CI jobs failures.

Change-Id: I1607e79beeee343893496efe01ca0be5ea684a9d
JIRA: VSPERF-271
Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Maryam Tahhan <maryam.tahhan@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: Brian Castelli <brian.castelli@spirent.com>