add to log anonymous maps instantiations that use overviews tables

Added to tiler profiler object:

overviewsAddedToMapconfig: true
mapType: 'anonymous'

test/acceptance/overviews_metadata.js

@@ -72,6 +72,7 @@ describe('overviews metadata', function() {
                   data: JSON.stringify(layergroup)
               }, {}, function(res) {
                   assert.equal(res.statusCode, 200, res.body);
+                  assert.ok(JSON.parse(res.headers['x-tiler-profiler']).overviewsAddedToMapconfig);
                   var parsedBody = JSON.parse(res.body);
                   assert.equal(res.headers['x-layergroup-id'], parsedBody.layergroupid);
                   expected_token = parsedBody.layergroupid;