adding definition for centos_7_x.sh using rhel7 puppetlab repo
Update centos_7_x.sh
Update centos_6_x.sh

Updating url according to https://docs.puppetlabs.com/guides/install_puppet/install_el.html
Update centos_5_x.sh

Changed url according to puppetlabs install page.
Merge pull request #30 from schrepfler/master

Adding a profile for CentOS/RHEL 7.x and updating 6.x and 5.x