lager_common_test_backend

Before every test, just `lager_common_test_backend:bounce(Level)` with the log level of your choice. Every message will be passed along to `ct:pal/1` for your viewing pleasure in the common_test reports. 

Also, you can call `lager_common_test_backend:get_logs/0` to get a list of all log messages this backend has received during your test. You can then search that list for expected log messages.

attn: @vagabond and friends
I don't remember. This was the way we did it in riak_test_lager_backend, and I believe there was some edge case that made this necessary. If the common_test version works without it, I'll fix it now.