riak_test_lager_backend was supporting Lager 2.0-style messages by
manually extracting and then reconstituting the pieces. It's much
easier just to pass it to lager_default_formatter, and then the format
is more declarative. Since we also have the opportunity to inject
newlines in each line as it is produced, we can skip the fold that
joined the log lines and simply convert it to a binary with the
unicode module.
* install a riak_sysmon custom handler and monitor for the busy_dist_port event on the riak node. when the handler detects the event it notifies the test process
* install riak_test_lager_backend on the riak node to capture log messages in memory. When the test process is notified that the busy dist port event fired on the riak node it retrieves the logs from the backend using the added get_logs/0 function and then checks for the busy_dist_port message
* there is a subtle race I *think*, that should rarely come up in practice, between lager and the riak_sysmon event handlers with this method of implementing the test that may require use of some form of retry/max retry still
