Support selecting default ruby for user

[deasmi]

I found this useful to select the default ruby once installed.

Happy for this to be included under the same license.

[DracoBlue]

+1

[DracoBlue]

I had to change it to:

exec { "su -l ${user} -c 'bash --login -c \"${command}\"'":

to make rvm current working. It failed since otherwise with:

RVM is not a function, selecting rubies with 'rvm use ...' will not work.

You need to change your terminal emulator preferences to allow login shell.
Sometimes it is required to use `/bin/bash --login` as the command.
Please visit https://rvm.io/integration/gnome-terminal/ for a example.