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
* 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
- Rename the 'Client' field to 'ClientInfo'
- Remove the 'expiry_interval' from session record
- Add more test cases for emqx_zone module
- Add more test cases for emqx_banned module
- Add more test cases for emqx_message module
- Remove 'sockname', 'conn_mod' fields from type 'client'
Zaiming Shi