improve test of Docker image

[vladak]

Currently the Docker image testing is very rudimentary and does not catch even basic errors in the entrypoint script (like when I specified wrong group for the chown done in the script and it instantly failed) so the current way

opengrok/dev/docker.sh

Lines 55 to 61 in 2c9ac25

	#
	# Run the image in a container. This is not strictly needed however
	# serves as additional test in automatic builds.
	#
	echo "Running the image in container"
	docker run -d $IMAGE
	docker ps -a

really needs to be replaced with something else.

[vladak]

Couple of ideas: let the container run for a bit with a known source root contents, then check the index presence, file ownership. Connect to the exposed port using the API (rather than with plain HTTP), perform some basic operations (search) and verify responses. Optionally check also with HTTP requests.

[vladak]

Also, check the logs. The logs could possibly be used for indication that the container has reached certain point. This can be done with Testcontainers, specifically https://testcontainers-python.readthedocs.io/en/latest/modules/generic/README.html, I believe.