ci: intermittent test failures in the integration tests jobs

[consideRatio]

Reported by @minrk in #861 (comment).

I guess without looking into it that this fixture could be to blame, because it is reloading hub / proxy, but does it ensure they are ready to be used after that?

1. proxy needs to be restarted and become ready
2. hub needs to be restarted and become ready
3. hub needs to configure routes in restarted proxy

Maybe if we ensure 3 is completed first, we reduce intermittent failures?

the-littlest-jupyterhub/integration-tests/conftest.py

Lines 9 to 29 in 05ed42a

	def preserve_config(request):
	"""Fixture to save and restore config around tests"""
	# Import TLJH only when needed. This lets us run tests in places
	# where TLJH is not installed - particularly, the 'distro check' test.
	from tljh.config import CONFIG_FILE, reload_component
	if os.path.exists(CONFIG_FILE):
	with open(CONFIG_FILE) as f:
	save_config = f.read()
	else:
	save_config = None
	try:
	yield
	finally:
	if save_config:
	with open(CONFIG_FILE, "w") as f:
	f.write(save_config)
	elif os.path.exists(CONFIG_FILE):
	os.remove(CONFIG_FILE)
	reload_component("hub")
	reload_component("proxy")