This will change the current hardwired PostgreSQL binary lookup mechanism to
utilizing the `pg_config --bindir` utility that should work better for most
distributions. The old method caused issues at least on Archlinux.
Changelog-None
Since we start a new instance of postgres for each test we may end up swamped
and the startup can take a bit longer. So let's loop until we get a success.
We had a couple of issues with workers dying and attempting to re-initialize
the database while it was already initialized. This will look for a free
directory and just start the DB in there, allowing workers to be better
isolated.
We'll rewrite the tests to use this infrastructure in the next commit.
Changelog-Added: The new `pyln-testing` package now contains the testing infrastructure so it can be reused to test against c-lighting in external projects
