JSON[io]: Modify the basic test for io.c

test/json_io.c: Refactored the structure and Add new test functions
for tee(),sendfile().
JSON[io]: Modify remaining parts of io.c

* io.c(sys_sendfile, sys_sendfile64, sys_tee, sys_splice,
sys_vmsplice, sys_ioctl): Modified to wrap the parameters in JSON format.
Because of the complexity of sys_ioctl(), the support is very limited and
not completed, need later fix on this syscall.
JSON[base]: Skip empty output in json_event_handler()

* json.c(json_event_handler): Check to see whether the
output string is empty, if it is empty then skip outputing
the quotes for empty string.