[WIP] Several small init script additions/improvements

The lack of configuration parameters like custom user home, or custom user and a weird startup/shutdown behavior on CentOS brought me to this PR.

**What did I change:**
- Added default file for init script to allow configuration for the runner
- Updated install area inside ReadMe.md
- Adapted the indention of the switch-case to match the rest of the script
- Renamed uppercase variables to lowercase vars
- Updated the check-if-Im-root-method to use the "new" EUID way
- Replaced `sudo` with `su -c` because on startup there is no tty where you can use `sudo` 
I will undo this change cause it messes up the code. But it is the source of the weird startup/shutdown beahvior on CentOS

- Edited the stop()-method to stop killing runners if there aren't any
There only was confusing output when stopping a stopped service because unnecessary code was executed. So I moved the rest of the method in a `else`-branch to get executed if runners exist.

- Remove PID-File when stopping
After a shutdown on CentOS the pid-file was not removed. When the server started again, there where pids inside which didn't exist. So it canceled the startup of the runners. I addded a `rm` command at the end of the method when everything went right.


**Testing:** 
I would be happy if more people could test/review it and let me know if anythign weird occured.
- [ ] Ubuntu 14.04 LTS 64bit
- [ ] CentOS 6.5 64bit