tool: Fix help message when is-configured fails

When is-configured fails for some modules, the help message suggested an
incorrect invocation:

    vdsm-tool configure module-name

Instead of the correct:

   vdsm-tool configure --module module-name

Change-Id: I417adfe55b3186418b61242b3ce63adcd5e9399e
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/31783
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>