We need this for /usr/bin/dbus-launch, which dconf tries to execute while
testing the Gio.Settings overrides in testGio.js.

Unreviewed, pushing to fix build.

This is phase 3 of the change to smaller Docker images and leaner CI.

Unreviewed; the only sensible review for this commit is whether the
builds succeed!

The only thing we now do while building Docker images with this script
is BUILD_MOZ, so just make the script always do that.

We aren't using jhbuild anymore, so we can install mozjs into a more
normal location such as /usr/local.

We only need the build dependencies for mozjs60, gjs, plus whatever
tools are needed in the CI scripts.

This seems unlikely to catch a problem that wouldn't be caught
elsewhere, and brings in a very heavy dependency.

The scripts are a lot smaller now that we build fewer images and don't
use jhbuild, so it's small enough to keep in one file. That makes it
easier to read.

We use "mozjs" everywhere else, so to remove any confusion about the
"SM" and "spider" abbreviations, rename the Docker images and the mozjs
build directory.

The 'fedora.static-analysis' image is now only necessary for cpplint, so
we create as small an image as possible using Alpine Linux to install
git and python, and then cpplint via pip.

We can't change the actual job yet, as the image will have to be built
first.

In the next phase we are planning to build the linter Docker image on
Alpine Linux instead of Fedora, which includes busybox by default
instead of bash. In order to keep the Docker image light, we don't want
to install bash on it; use only POSIX shell syntax in the test-ci.sh
script.