QError: Add errors needed by QMP

Only QERR_QMP_BAD_INPUT_OBJECT is QMP specific, the others can
be used in different contexts by other subsystems.

Please, note that QERR_JSON_PARSING signals any parsing error
from the json parser. We will need it until the parser gets
updated to use QError.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>