This causes `upgrade-zulip-from-git`, as well as a no-option run of
`tools/build-release-tarball`, to produce a Zulip install running
Python 3, rather than Python 2. In particular this means that the
virtualenv we create, in which all application code runs, is Python 3.
One shebang line, on `zulip-ec2-configure-interfaces`, explicitly
keeps Python 2, and at least one external ops script, `wal-e`, also
still runs on Python 2. See discussion on the respective previous
commits that made those explicit. There may also be some other
third-party scripts we use, outside of this source tree and running
outside our virtualenv, that still run on Python 2.
We document the `deployment.git_repo_url` setting in `/etc/zulip/zulip.conf`
to control where this script fetches from, and don't say that it's
only read on the first such upgrade and cached thereafter. The documented
behavior seems like the right behavior. So use the currently configured
URL every time, by writing it anew into the config of our cache repo.
rht
Greg Price
Tim Abbott