Adding support to not enable the gradle daemon by default

Hello! Thanks for the awesome work on this and releasing it as open source.

I've added a few tests here around the generated `/etc/profile.d/gradle.sh`. 

I had a few problems getting started running the test suite because all of the gems listed have had several releases since being added and the Gemfile.lock is not checked in. After running a `bundle install` and getting things working, I added `~>`'s to each version, since we know these work together and patch-level updates shouldn't change that.

The change I was looking to write a test for and make is adding a `daemon` parameter to the gradle class. I've had just enough trouble with the gradle daemon caching that I prefer to run with it off. I'd like to use this module for installing on a CI box, where I'd always like the daemon off.

The default remains for the daemon to be on, so no current users should be in for any surprises.