initscript: pass complete path to pidfile to status command

initscript: pass complete path to pidfile to status command

Older versions of RHEL/CentOS used pifof in preference to the pidfile
and hence we got away with passing just the basename instead of
including the full path. Using pidof first doesn't make much sense and
this was fixed in RHEL 5 update 4 (see https://bugzilla.redhat.com/show_bug.cgi?id=440658)

This means that on RHEL 5.4 "service vswitch status" always returned
"ovs-vswitchd is stopped" even if it was running. Fix this issue by
passing in the correct pidfile name.

Cross-port of Ian Campbell's commit d1c8c9e4 on xs5.7 branch.