Fix one-shot commands for a specific container being executed using host environment variables

[maurobender]

With this change the one-shot commands run from the UI use the environment variables from the container instead of the host.

Closes #2172.

Example:

Container env vars:

One-shot command using env vars from the container works as expected now:

String quoted is executed correctly:

[andrasbacsai]

Thank you for the PR! I will test it if everything works as expected!