Fix PHP conf dir for Ubuntu 14.04

This consider the new PHP conf.d directory structure for Ubuntu 14.04 LTS. Basically, now we don't have the base conf.d dir anymore.

 This is working, but it's just a first path. Somethings that I don't like about it:

* The `unless` check for `newrelic.ini`
* I had to change `$newrelic_php_conf_dir` to an array

Feedback welcomed!