[COOK-3470] Improvements in /etc/mavenrc template

Related to http://tickets.opscode.com/browse/COOK-3470

**Notes about noisy git commit history**

I initially started in mind to extend work from @jlandahl (see PR #21 / COOK-3352) and that's why this feature branch *currently* started from commit 97afb5b (from #21). I also wanted to address similar issues as @jblatt-verticloud did in PR #9. Thank you everyone for your pushed stuff, I hope you'll like my solution...
After giving some whirl to the code, it resulted with something quite more simpler (in my opinion), but that should meet most use cases. What do you think? 

If this patch is accepted, let me know if you prefer I drop no more relevant commits and rebase into a single commit.