Add a user variable to templates

This is a common configuration option and allows devstack (and others)
to configure a mod_wsgi user to run the daemon process.

Change-Id: Idf134b3bc6b08e3c3a80dde8830d5a4f3da5a06c
Fixes: bug 1226346
Fix probe tests

Change-Id: I03573bf24baf031b1874c3ff2e2d89d34473c266
add seek() to CompressingFileReader

Change-Id: I33d9119684497b53101db3bc380953e86bdf25f0
Merge "add seek() to CompressingFileReader"
Merge "Add a user variable to templates"