Monitor all sensor types by default to rtorrent

[riptl]

Description:

After merging #17421, @MartinHjelmare commented:

I just realised that this shouldn't have an empty list as default if this config option is optional. Either have it be optional and default to all conditions, or make it required and remove default.

This PR adds all three sensor types to monitored_variables, if the user omits the field in the configuration.

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox.

[houndci-bot]

Some files could not be reviewed due to errors:

Traceback (most recent call last):

Traceback (most recent call last):
  File "/home/linters/.local/bin/flake8", line 7, in 
    from flake8.main.cli import main
ModuleNotFoundError: No module named 'flake8'

[houndci-bot]

Some files could not be reviewed due to errors:

Traceback (most recent call last):

Traceback (most recent call last):
  File "/home/linters/.local/bin/flake8", line 7, in 
    from flake8.main.cli import main
ModuleNotFoundError: No module named 'flake8'

[houndci-bot]

Some files could not be reviewed due to errors:

Traceback (most recent call last):

Traceback (most recent call last):
  File "/home/linters/.local/bin/flake8", line 7, in 
    from flake8.main.cli import main
ModuleNotFoundError: No module named 'flake8'

[MartinHjelmare]

Great, thanks!

[MartinHjelmare]

Can be merged when build passes.

[houndci-bot]

Some files could not be reviewed due to errors:

Traceback (most recent call last):

Traceback (most recent call last):
  File "/home/linters/.local/bin/flake8", line 7, in 
    from flake8.main.cli import main
ModuleNotFoundError: No module named 'flake8'

[riptl]

Travis CI builds are stuck again :/

[MartinHjelmare]

I cancelled and restarted.

[riptl]

Thanks, but it still seems to be stuck on Created 🤔
Let's just wait it out.