SBUS ERRORS: Add unknown domain Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

SBUS: Add data provider errors Reviewed-by: Sumit Bose <sbose@redhat.com> Reviewed-by: Jakub Hrozek <jhrozek@redhat.com> Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>

sbus: provide custom error names Errors provided directly by D-Bus are not sufficient to fulfill all our needs. Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>