Healthcheck url from json (#1868)

* Get healthcheck URL from JSON file

Obtain Jupyter server's full URL from
/home/$NB_USER/.local/share/jupyter/runtime/*.json
and use it for healthcheck.

* Expand tests for healthcheck

* Update pre-commit config

* Remove workdir from tests

* Wait for container start with 0.1s interval

* Quote NB_USER variable on base-notebook/Dockerfile

* Fix style and make test actually work

* Ooops, GitHub didn't show last line

* Fix mypy

* Use bash with pipefail option for healthcheck

* Create python script for healthcheck

* Don't verify SSL certificate on healthcheck

* Update healthcheck test

- Add "user" parameter
- Add tests when container should not be healthy

* Fix typo

* Update test_healthcheck.py

---------

Co-authored-by: Ayaz Salikhov <mathbunnyru@users.noreply.github.com>

base-notebook/docker_healthcheck.py

@@ -0,0 +1,18 @@
+import json
+import os
+
+import requests
+
+# A number of operations below delibrately don't check for possible errors
+# As this is a healthcheck, it should succeed or raise an exception on error
+
+runtime_dir = "/home/" + os.environ["NB_USER"] + "/.local/share/jupyter/runtime/"
+file_list = os.listdir(runtime_dir)
+json_file = [s for s in file_list if s.endswith(".json")]
+
+url = json.load(open(runtime_dir + json_file[0]))["url"]
+url = url + "api"
+
+r = requests.get(url, verify=False)  # request without SSL verification
+r.raise_for_status()
+print(r.content)