tool: Fix TypeError when configuration check fails

When is-configured and validate-config failed for some modules, we got a
TypeError trying to join a list of configurator objects, instead of list
of strings.

    TypeError: sequence item 0: expected string, Sanlock found

Change-Id: Ic2fde1ddbbb9584429a4c190d38a2817e5a6dfb1
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/31782
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: mooli tayer <mtayer@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>