[dnf] Collect module --list and use collect_cmd_output content

[TurboTurtle]

This is a 2-patch set that:

1. Updates dnf to use the output key of the collect_cmd_output() dict instead of re-reading the file into memory.
2. Adds dnf module list to collection, not just dnf module list --installed as requested in RHBZ#1781819

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