main: support lock pid file arg

This patch adds support to change the default corosync pid file lock
path. This is useful to run corosync net namespace environment only and
since the pid lock file cannot be clarified over the conf because the
pid lock file exists before config parsing we allow the user to specify
it over the command line.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>