Instead of instructing users to do static calls
in to Unleash, she should instead be allwed to
specify the log provider as an option to Unleash.
This commit introduces the "getLogger" option,
a function responsible for creating a logger.
Currently if the intial metrics-fetch fails unleash will not
setup a metrics-poller. This fix ensures that the metrics
poller will start regardless of whether the inital fetch
fails or succeeds.
closes#396
