csaf_validator: Warn if remote_validator is not configured

[s-l-teichmann]

The validator only validates against the JSON schema if the remote validator is not configured.

In this case a warning should be issued.

[tschmidtb51]

We should also consider the exit codes. Suggestion:

• 0: all valid
• 2⁰: schema invalid
• 2¹: no remove validator configured
• 2²: failure in remote validation

[bernhardreiter]

Would it be a plus to run the JSON schema validation in any case? This would eat some CPU cycles, but may potentially catch differences in the schema validation codepaths between the csaf_validator and the remote validator.

[bernhardreiter]

More about the use case from @tschmidtb51:
He wants to use the exit code in scripting (e.g. bash scripting) to make a distinction between the suggested situations and their combinations.

We should introduce an 1 aka 2⁰ as general failure exit code and move the other ones one bit left.