Update for doc-tools 0.6

We can do now everything in the tox file and thus minimize the
content in the jenkins file.

This needs sitepackages set since gneratedocbook needs xml2po
which cannot be installed in the venv. Since it's installed in
the system, let's use sitepackages.

Change-Id: I8c9d578c069ecd55ce9c6abe9e8d48e666962c20