Fail test suite on unhandled promise rejection [API-1604]

In the past I faced several places where we weren't handling promise rejections properly. In future version of node, it's very likely that it will start throwing on unhandled promise rejections, so, we need to make sure that there are no such places in the library code base, as well as in the test suite. The proper way should be to log details of the rejection and stop the [process](https://nodejs.org/api/process.html#process_event_uncaughtexception) with an error code.