* Add more test cases for emqx_stats and emqx_os_mon
Fix test case error for emqx_ws_connection
* Add more test cases for emqx_sys_mon
* Update erlang otp to 22.1 for travis ci
* Delete readable=false for make ct
* Add unset_all_env for emqx_zone and update test cases
* 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