[site_cubicweb] add options to contact elasticsearch to config

site_cubicweb.py

+options = (
+    ('elasticsearch-locations',
+     {'type': 'string',
+      'default': '',
+      'help': 'Elastic Search location (eg. 192.168.0.23:9200), '
+              'this can be a list of locations (192.168.0.23:9200,192.168.0.24:9200,'
+              ' you can also include the scheme (eg. http://192.168.0.23:9200) ',
+      'group': 'elasticsearch',
+      'level': 5,
+      }),
+    ('index-name',
+     {'type': 'string',
+      'default': 'cubicweb',
+      'help': 'Elastic Search index name (eg. cubicweb)',
+      'group': 'elasticsearch',
+      'level': 5,
+      }),
+)