[Android] Enable instrument test for Contacts API.

Enable instrument test for Contacts API. And, fixed some issues in
contacts test case. The callback function of Promise is invoked after
oncontactchanges(). So, testNewContactFlag will be false. The test
always fail.
It is possible that this flag never set to true: when this callback is called earlier than the one in `contacts.save(contact1).then()`

Can put it into the `then()` above to avoid such case.