HostKSM: Gracefully handle ksmd pid lookup failure

In case the pid of ksmd cannot be found we currently fail with a
ValueError exception.  Check the pidof return code before trying to
convert the output to an int.  If the pid cannot be found, then report 0
for get_ksmd_jiffies().

Change-Id: Iccd14ee44f4f7d8d9107e692c9faa27e7c487790
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1152182
Signed-off-by: Adam Litke <alitke@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34378
Reviewed-by: Francesco Romani <fromani@redhat.com>