Change ownership of the Wolfplex datastore to php-fpm user

Summary:
The datastore is for the php-fpm wolfplex process,
and so for web-org-wolfplex-www instead of the static web
user wolfplex.org.

This is a follow-up for change 2f6980f3f62f.

Test Plan:

$ sudo -u web-org-wolfplex-www rlwrap psysh
>>> $_ENV['DATASTORE'] = '/var/dataroot/wolfplex';
=> "/var/dataroot/wolfplex"
>>> $fd = fopen($_ENV['DATASTORE'] . '/2013.txt', 'a');
=> stream resource #297

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1467