Make PEAR a little smarter.

This lets PEAR still work if provisioning is re-run. It seems to work as-is even though
it's an array; at least, it has for me. Inspired by:
http://stackoverflow.com/questions/20804004/installing-php-pear-packages-via-ansible-with-idempotency
https://github.com/geerlingguy/ansible-role-php-pear/blob/master/tasks/main.yml