Fix logging level of __virtual__() module

[foklan]

What does this PR do?

What issues does this PR fix or reference?

Fixes

Previous Behavior

Error messages from module __virtual__() were logged at error level.

New Behavior

Error messages from module __virtual__() are logged at debug level.

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

No

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[dwoz]

Use tests.support.helpers.dedent instead