Consider moving logging over to lager. [JIRA: RIAK-1918]

[evanmcc]

Because we're getting filtered/rate-limited in certain situations (see error messages in basho/riak#517), and backpressure might serve us better. Lager is already a dep, so maybe might as well use it? Or perhaps a logging macro, so the user can decide at compile time which system they'd like to use.

[bsparrow435]

This has been requested by customers as well so that all common logs(such as bitcask merge messages) can be easily groked with logstash and other 3rd party tools. The lager built in formatter if very nice for this functionality