This will hopefully make CI runs more robust and recover stale workers.

This is required to build the next branch which requires rsync to be
available.

Rsync is a requirement for OpenWrt master and therefore our next
branch. Currently builds on x86-64 error out due to missing rsync:

/bin/sh: 1: rsync: not found

This enables build-testing only on master as well as next and release
branches.

This will be a useful precursor for continuous integration.

The gluon-web package is basically a stripped-down and refactored version
of the LuCI base.

This script will analyze the dependencies of Gluon's packages and output
them as a dot graph.