When dialing a phone number, also look to see if there's a corresponding
native user for the resulting user, and if so, go to the native room
for that user.
This is out first CallHandler test(!) Switches react-sdk to use
createCall on the client object so we can stub this out in the test.
Add a bunch more stubs to the test client.
There's more stuff in this test that has scope to be used more
widely, like waiting for a certain dispatch and mocking out rooms
with particular sets of users in them: we could consider moving these
out to test utils if we wanted.
David Baker