admin rewrite: make OMERO.tables module configurable

Add @omero.tables.module@ to the list of templates to be substituted
in the server IceGrid XML templates and replaces it with the
value. of `omero.tables.module` in the OMERO configuration, using
`runTables` as the default.

This change should be a no-op when used with OMERO.server binaries up
to 5.6.11 but will be mandatory once the templates are updated to
use the new substitution field.

src/omero/plugins/admin.py

@@ -1198,7 +1198,9 @@ def clear_tail(elem):
             '@omero.ports.registry@': config.get(
                 'omero.ports.registry', '4061'),
             '@omero.master.host@': config.get('omero.master.host', config.get(
-                'Ice.Default.Host', '127.0.0.1'))
+                'Ice.Default.Host', '127.0.0.1')),
+            "@omero.tables.module@": config.get(
+                "omero.tables.module", "runTables")
             }
 
         client_transports = config.get('omero.client.icetransports', 'ssl,tcp')