qapi: output def_value_str when query command line options
Change qapi interfaces to output the newly added def_value_str when querying
command line options.
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Leandro Dorileo <l@dorileo.org> Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com> Signed-off-by: Chunyan Liu <cyliu@suse.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>