libxl_json: Enable yajl_allow_trailing_garbage

libxl_json: Enable yajl_allow_trailing_garbage

This allows to parse a string that is not NUL-terminated. With that
option disabled, YAJL v2 would look ahead on completion to find out if
there is more to parse.

YAJL v1 doesn't have this behavior.

Any function that allocates a yajl_handle via this function either parse
a NUL-terminated string, or do provide proper length. So change the
default and allow garbage (like a different JSON document) after the end
of the data to parse.

This is important for the QMP client, as there could be more than one
message to parse, and YAJL would consider the next message to be garbage
and throw an error.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>