And move emqx app back to root level
After realising the challenges of developing plugins in standalone
rebar projects. it is perhaps more smooth to keep using emqx as
a rebar dependency
* Fix the Exit in testcases
* Fix Exit in emqx_mod_sup_SUITE
* Update testcases for log_tracer
* Fix Exit in emqx_protocol_SUITE
* Add will_acl_check
* Fix more Exits