For some reason, the CI runs on Github Actions block the macOS runners,
and they take forever to run the tests. The tests are really needed only
on Linux, and the errno values that it uses are only verified to work on
Linux.
This change adds an automated test harness that will spin up an instance
of the X52 daemon, connect to its command socket, send commands and
validate the responses. This first set of test cases simply validates
the basic configuration file handling. Subsequent commits will enhance
the tests to improve code coverage.