Add comments & enable bosh_SUITE, update login_SUITE

I enabled `bosh_SUITE` and annotated the  `cant_sent_invalid_rid/1` test case to make it clear that errors will be logged by the server.
`login_SUITE` was extended to work with modern escalus.
`system_monitor_SUITE` was marked as pending -- they contain hard-coded node names which are no longer valid.
The tests in `metrics_roster_SUITE` leave some state on the server(?) and interfere with one another. I changed their order and marked the issue for investigation.