Error message when token cache persistence fails could be more descriptive

[christothes]

This error

"Persistence check failed. Data was written but it could not be read. Possible cause: on Linux, LibSecret is installed but D-Bus isn't running because it cannot be started over SSH."

could be more descriptive and accurate as it applies to various platforms. In addition the exception behavior is inconsistent (on Linux we don't throw exceptions, we just log them).