fix permission error on CentOS

fix permission error on CentOS 6.5

errors occurred like this:

```
TASK: [newrelic | RedHat | Add the New Relic repository key] ****************** 
failed: [xxx.xxx.xxx.xxx] => {"failed": true, "item": "", "md5sum": "be9704aa1e7001d855a60c4c05d7598b"}
msg: Destination /etc/pki/rpm-gpg not writable

FATAL: all hosts have already failed -- aborting
```

```
TASK: [newrelic | Configure New Relic Sysmond] ******************************** 
failed: [xxx.xxx.xxx.xxx] => {"failed": true, "item": ""}
msg: Destination /etc/newrelic not writable

FATAL: all hosts have already failed -- aborting
```

```
TASK: [newrelic | Ensure New Relic Sysmond is started and enabled] ************ 
failed: [xxx.xxx.xxx.xxx] => {"failed": true, "item": ""}
msg: ERROR: must run /etc/init.d/newrelic-sysmond as root


FATAL: all hosts have already failed -- aborting
```