Stage phpBB 3.2

Summary:
The phpBB SaaS relies on Docker containers with phpBB code inside,
and datastores containing the mutable directories like config, ext,
files, images and store.

When a new datastore is created, it needs to be bootstraped with
the current phpBB upstream content. Salt will use those staged
files to deploy config/ ext/ files/ images/ and store/.

Ref T1377.

Test Plan:
file.recurse with salt://software/phpbb/phpBB/{{ subdir }}
as source in D1520

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1377

Differential Revision: https://devcentral.nasqueron.org/D1519