util/error: do not free error on error_abort

It would be nice to have Error object not freed away when debugging a
coredump.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20190415142519.73060-1-vsementsov@virtuozzo.com>
[error_printf_unless_qmp() replaced by error_printf()]
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>