* [common] Make dolphinscheduler_env.sh work

* Change dist tarball `dolphinscheduler_env.sh` location
  from `bin/` to `conf/`, which users could finish their
  change configuration operation in one single directory.
  and we only need to add `$DOLPHINSCHEDULER_HOME/conf`
  when we start our sever instead of adding both
  `$DOLPHINSCHEDULER_HOME/conf` and `$DOLPHINSCHEDULER_HOME/bin`
* Change the `start.sh`'s path of `dolphinscheduler_env.sh`
* Change the setting order of `dolphinscheduler_env.sh`
* `bin/env/dolphinscheduler_env.sh` will overwrite the `<server>/conf/dolphinscheduler_env.sh`
when start the server using `bin/dolphinsceduler_daemon.sh` or `bin/install.sh`
* Change the related docs