This commit changes all QERR_ macros to contain a human message (ie.
the desc string found in qerr_table[]) instead of a json dictionary
in string format.

Before this commit, error_set() and qerror_report() would receive
a json dictionary in string format and build a qobject from it. Now,
both function receive a human message instead and the qobject is
not built anymore.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>