Fixing typos in Redhat.yml filenames

Small typos fixed, there were errors before:
```
fatal: [all] => input file not found at /etc/ansible/playbooks/statserver/roles/graphite/vars/RedHat.yml or /etc/ansible/playbooks/statserver/RedHat.yml
```
```
fatal: [all] => input file not found at /etc/ansible/playbooks/statserver/roles/sentry/vars/RedHat.yml or /etc/ansible/playbooks/statserver/RedHat.yml
```