Make tests wait for syncs to happen

Add lots of calls to `syncPromise` to cope with the fact that sync responses
are now handled asynchronously, which makes them prone to races otherwise.

Also a quick sanity-check in crypto to make one of the test failures less
cryptic.

spec/integ/matrix-client-crypto.spec.js

@@ -691,7 +691,7 @@ describe("MatrixClient crypto", function() {
                         [bobUserId]: {},
                     },
                 });
-                return aliTestClient.httpBackend.flush('/keys/query', 1);
+                return aliTestClient.httpBackend.flushAllExpected();
             });
     });