Building Ubuntu Click applications - minimal package built manually

Note: This has been obsoleted by the move from schroot to LXD. See this post.

There is some information available on the Ubuntu developer portal on building Click applications. But this mostly covers pure QML applications or QML applications with a C++ shared library, all with the Ubuntu SDK IDE (rebranded Qt Creator).
If you care about what is happening below this level, there is not that much info available, at least not in one place. I found:

Building an ethernet tap with linux

Say you want to see what's going on an ethernet line. And say the line runs something like PPPoE, i.e. a protocol below the internet layer, where the addressing is done by MAC addresses.

It's not possible to put an ordinary switch in the middle, as the ethernet frames would not get through. What is needed is an ethernet tap or port mirroring. An old-fashioned ethernet hub would work here, mirroring the traffic from either end of the original wire to a third port that could be monitored e.g. by Wireshark. But can this done be without a special device, with plain linux?