Add osmium to mediawiki-installation

* osmium needs to be a scap target so we can use it as a test job runner for
  testing HHVM in production.
* it has the requisite software components configured via puppet.
* I deployed scap to it earlier.

Change-Id: Ieec5ffc4c5d3f7724aa9e0f9a6ad5d9edd4fde4c