The docker installer configuration incorrectly had has_appserver set
to 0; this meant that (A) the docker-zulip code needed to copy the
block of code in the installer for the `has_appserver` case into the
Dockerfile (unnecessarily), and (B) one couldn't use `install` from a
Git ref (because the static asset compiler didn't end up in the right
place).
It appears that docker-zulip tried to set this flag in their `install`
command line, but the construction inside `install` meant that didn't
work.