Switch our fast_log for lager in reltool config

Adds lager as a dep in erchef and removes fastlog.

No other actions taken in the erchef dir, but also see PR in omnibus-chef-server and chef_wm.

It is unclear to me if the erl_opts in the rebar config need to be updated to include the lager transform, as I'm not clear on how rebar handles erl_opts between top level projects and dependencies. Clarification appreciated as I work on testing these changes.