This seeks to fix the intermittent failure of the "MatrixClient rehydrated from
stored credentials" tests.
The problem appears to be that the 'load_completed' is sometimes taking a while
to come through from the dispatcher - or rather, it is taking a long time to
get *sent* to the dispatcher: the chain of `q().then().catch().done()` in
componentDidMount can take a while to happen.
As a workaround, give the test a few goes when waiting for us to start
syncing. It's not ideal to be poking into the internal state of MatrixChat like
this, but it'll do for now.
597705716b