Some tests may not spawn a node at all, so make sure that our assumption that
the directory exists in the fixture cleanup is correct by creating the
directory.

We roll the `elements_add_fee_output` function and the cropping of
overallocated arrays into the `bitcoin_tx_finalize` function. This is supposed
to be the final cleanup and compaction step before a tx can be sent to bitcoin
or passed off to other daemons.

This is the cleanup promised in ElementsProject#3491

`pylightning` is not much more than an alias for `pyln-client`, so this
removes the need to install that as well just to run the tests.

For some reason we fail to remove the test directory in some cases. My
hypothesis is that it is a daemon that is not completely shut down yet, and
still writes to the directory. This commit intercepts the error, prints any
files in the directory and re-raises the error. This should allow us to debug
the reappears.

pytest captures the output by monkey patching out `sys.stdout`. This may
conflict with our use of `sys.stdout` when configuring logging, resulting in
the "Write to closed file" issue that is spamming the logs. By making the
logging configuration a fixture hopefully we always use the correct
stdout (after pytest has monkey-patched it).

Looking for specific feerates, but not adjusting the amounts involved doesn't
work.

Postgres does not guarantee that the insertion order is the returned order,
which leads us to skip outputs that have already been stolen onto the selected
utxos set, but not added to it because it isn't confirmed. This may also
happen with sqlite3 though it's a lot rarer in that case.

Constants once again.