fix bug in goalless configs
add tests to try and cover unexpected failures
minor format refactoring
provide the erlang lib dir and cwd as working libraries

This happens for every call unless the user passes
--disable-default-libs to relcool or {disable_default_libs, true} in
the relcool config.
make common_test support explicit

The rebar support for common test is very, very buggy and it fails
often without common_test failing due to how rebar integrates with
common test. This patch takes the responsability for running common
test from rebar and runs it directly.
change the default log level to info

This makes it a bit more comforting to the user (and me as well). With
this the user sees a short description of the release.