rotate_api_key --user non-existing in cli should print correct message

[orenbm]

In the cli when you run the following command:
rotate_api_key --user non-existing
the message is:
Unable to authenticate with Conjur. Please check your credentials.

the correct message should indicate that the user non-existing doesn't exist.

[eladkug]

@shaharglazner can we send message "user non-exisitng" from security perspective ?

[sashaCher]

There's no security aspect in writhing right message if non-existing user does not exist and user that runs rotate_api_key command is an authenticated user.