Add flag --log-credentials-errors

[dcermak]

Currently container-suseconnect will print errors to the console when it fails to obtain the SLE credentials. This is however causing UX issues in the SLE BCI containers, which work perfectly fine without a SLE subscription.

Thus a new flag is introduced: --log-credentials-errors. When this flag is set or if the environment variable CONTAINER_SUSECONNECT_LOG_CREDENTIALS_ERR is set, then container-suseconnect will continue printing errors as it did, but the default is now that errors with obtaining the credentials will be silently swallowed so that users of SLE BCI don't get confused by this error message.

This fixes https://github.com/SUSE/container-suseconnect/issues/62

[dirkmueller]

As a user/customer, the behavior I would expect is

• if a registration credential is available, and the requestProducts is failing, then I'm a registered customer with some kind of issue (network accessibility, or expired/invalid key or the like). I totally want to see errors by default, and maybe optionally have the option to suppress the error with --ignore-whatever-is-wrong-with-my-key option
• if no registration credentials are available, the product service listing can fail because there is an authentication issue, but that's okay in the BCI case because there is a fall back repository that does not require a credential.

This patch is putting the burden of finding out which case it is on the user, and it changes the default to the second, unregistered option. Following the 'supported customers first' principle I am wondering if we can do something to make the first option also as convenient. can we keep the default of the behavior, but handle only the case of "BCI repository available and no registration code provided" silently instead?

Detecting whether "BCI repository available" could be done by calling this via a new name that enables the new behavior, so existing invocations remain unaffected.