Sometimes apt will fail due a transient network issue. Often that
will be fixed by retrying.
This is particularly useful as part of an automated build pipeline.
sysv-rc and util-linux are used in the postinst scripts
of some packages, and so those packages won't install
if they aren't available.
sysv-rc contains update-rc.d, so any package that installs
a service would fail to install. Those packages are common
to install in to containers.
util-linux contains the getopt command which some scripts
expect to find.
Some licences require that the binaries be shipped with a copy
of the license. Debian does this in the copyright files in
/usr/share/doc. We need to leave those files there to keep
the image distributable.
If master builds successfully then push the results
to dockerhub.
We assume that the dockerhub username and password will
be in the environment. This will use travis env vars so
that the secrets aren't available to forks.
The on: branch: master means that other branches wouldn't
push to dockerhub.
James Westby