Fix image pull overwriting pre-loaded images and missing PYTHONPATH

Two bugs:

1. pull_or_build_image always called client.images.pull() which pulls
   from the registry even when the image was already loaded into the
   node via docker save | docker load in CI. This overwrote the
   locally-built image (containing the /var/log/mysql fix) with the
   published GHCR version that lacks it, causing mysql entrypoint to
   fail with Permission denied. Fix: check images.get() first and only
   pull/build if the image is not already present locally.

2. exec_command over SSH runs in a non-login, non-interactive shell
   which does not load ~/.profile or PYTHONPATH, so pip --user packages
   at ~/.local/lib/python3.10/site-packages are not found. This caused
   ModuleNotFoundError: No module named 'docker' when running
   container.py remotely. Fix: prepend PYTHONPATH explicitly.

Author: szachovy

src/container.py

@@ -103,9 +103,12 @@ def __init__(self, container: str | None) -> None:
     @staticmethod
     def pull_or_build_image(client: docker.client.DockerClient, image: str, build_context: str) -> None:
         try:
-            client.images.pull(image)
-        except (docker.errors.DockerException, requests.exceptions.RequestException):
-            client.images.build(path=build_context, tag=image)
+            client.images.get(image)
+        except docker.errors.ImageNotFound:
+            try:
+                client.images.pull(image)
+            except (docker.errors.DockerException, requests.exceptions.RequestException):
+                client.images.build(path=build_context, tag=image)
 
     def run_command_on_the_container(
             self,

src/remote.py

@@ -125,7 +125,9 @@ def run_python_container_command(self, command: str) -> dict:
         ) as memfile:
             source = memfile.read() + command
         self.upload_file(content=source, remote_file_path=f'/opt/{nonce}.py')
-        _, stdout, stderr = self.ssh_client.exec_command(f"python3 /opt/{nonce}.py")
+        _, stdout, stderr = self.ssh_client.exec_command(
+            f"PYTHONPATH=/home/superset/.local/lib/python3.10/site-packages python3 /opt/{nonce}.py"
+        )
         result = {
             "output": stdout.read().decode(),
             "error": stderr.read().decode()