Better support for Mac/Linux users

Hengwen Zhangrequested to merge
docker into master

Users now can choose to start RMI server on different port if they want. This let them run multiple RMI server on a machine.

If the chosen port is unavailable, the program will give an explicit message to indicate user the reason.

The scripts for starting the RMI server on both windows and mac/linux machines has been tested.

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