Install nginx on PaaS Docker servers

Summary:
For the paas-docker role the nginx unit provides configuration
for the vhosts matching deployed containers, but don't install
nginx itself.

Plan is to install and configure nginx fully automatically.

Ref T1595

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1595

Differential Revision: https://devcentral.nasqueron.org/D2223