Clarify log message for missing caps

[jnodorp]

Description

Changed warning to error.

Motivation and Context

Confusing container exit without errors.

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[yubiuser]

I think I don't understand your motivation. Without the capabilities, FTL would not run anyway - why not stop the container already at startup then?

[rdwebdesign]

Running the container without capabilities is not possible.

This is exactly why we should exit in case the system is unable to set capabilities. The container will fail anyway.

[jnodorp]

Sorry, just started out w/ pihole. Then the bug is the warning vs. error message. I updated the PR accordingly.

Having the container exit (seemingly) without an error was confusing.