Try not to load imagery when running tests

By default, the `rendererBackground` code will choose an initial imagery based on what
sources are available at the given map location. It looks like this code will fallback
to "custom" _before_ "none", and I noticed that in some cases it was trying to fetch
whatever source happened to be stored in the "custom" template in localStorage.

This commit adds an explicit window.location.hash in a few places to encourage the
background layer to be "none". Some tests do change the hash, so this isn't perfect.

test/spec/modes/add_note.js

@@ -2,6 +2,7 @@ describe('iD.modeAddNote', function() {
     var context;
 
     before(function() {
+        window.location.hash = '#background=none';  // Try not to load imagery
         iD.services.osm = iD.serviceOsm;
     });
 

test/spec/spec_helpers.js

@@ -5,6 +5,9 @@ iD.debug = true;
 // Disable things that use the network
 for (var k in iD.services) { delete iD.services[k]; }
 
+// Try not to load imagery
+window.location.hash = '#background=none';
+
 // Run without data for speed (tests which need data can set it up themselves)
 iD.fileFetcher.assetPath('../dist/');
 var cached = iD.fileFetcher.cache();