fix broken yumrepo in puppet::repo::puppetlabs

the yumrepo resource is broken:
https://tickets.puppetlabs.com/browse/PUP-2782

this commit will create a repo file based on
http://yum.puppetlabs.com/puppetlabs-release-el-6.noarch.rpm
so you can use this module also on nodes that have this rpm installed
(otherwise you would declare the repos twice which would confuse yum)