add support of short format in tracer.json

To make it more easy to add trace to tracer.json, introduce short
format for kprobe.

Now, you can use "ip_rcv:0" instead of:

{
	"name": "ip_rcv",
	"skb": 0
}

Simpier, isn't it?

The old format is still supported for complex case.

Signed-off-by: Menglong Dong <[email protected]>