New Relic Repo only has reference to EL

[wbates]

The current New Relic Repo url has a variable of $releasever. However, New Relic only maintains a static 'el5' directory in that place which it documents to be used with all supported versions of RHEL and CentOS (5 and 6).

Until they add an official path on their yum server for the various versions, it may be best to hard code this to 'el5'.