Repo enhancements (yum)

Hello,

I made some enhancements to support a customizable repo location. Let me know if you'd like to see anything different!

File created by newrelic-repo package:
% cat newrelic.repo
[newrelic]
name=New Relic packages for Enterprise Linux 5 - $basearch
baseurl=http://yum.newrelic.com/pub/newrelic/el5/$basearch
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-NewRelic

File created with PR and default attrs:
% cat /etc/yum.repos.d/newrelic.repo
# This file was generated by Chef
# Do NOT modify this file by hand.

[newrelic]
name=New Relic packages for Enterprise Linux
baseurl=http://yum.newrelic.com/pub/newrelic/el5/x86_64
enabled=1
gpgcheck=1
gpgkey=https://raw.githubusercontent.com/escapestudios-cookbooks/newrelic/master/files/default/RPM