Replace calls to docker_exec to support SSH access alternatively

[ckunki]

Currently ITDE uses docker_exec to access the Docker Container, e.g. to analyze the content of some logfiles. With version 8 and higher the format of the Docker Containers might change so that docker_exec is no longer possible. Instead ITDE will then need to use SSH access.

Ticket #301 already requested to detect the version number of the Exasol database inside the Docker Container and to decide whether to use docker_exec or SSH access.

The current ticket requests to replace all existing calls to docker_exec in ITDE by calls to an abstraction the enables to use either docker_exec or SSH access. The abstraction needs to be aware about the current docker flavor detected in ticket #301 in order to use the appropriate access method.

AC

1. All calls to docker_exec are replaced by an abstraction
2. incl. docker_db_log_based_bucket_sync_checker.py
3. The abstraction uses the detected flavor of the current Docker Container detected in ticket #301

[ckunki]

is_database_ready_thread.py tries to execute an SQL command until the database responds.

Analysis showed

• Before the try context in line 45 fabric.Connection().run() fails with NoValidConnectionsError "Unable to connect".
• After successful database startup in line 64 fabric.Connection().run() succeeds.

For me this currently seems to have the consequence that ITDE cannot use SSH executor to find exaplus SQL client nor to detect whether the database is up and running.