Switch our fast_log for lager in reltool config
Add REBAR_PARENT to makefile

This will be used by the rebar.config.script in chef_wm
to merge erl_opts between base projects and dependent projects
instead of causing any overwrites. Only happens if REBAR_PARENT
is set however, so make sure it is set here.
Merge branch 'mm/move-to-lager'