Bug: MQ error when subscribing path is long

[quwenjie]

This bug is discovered when I call cl.get_variable with a slightly long key, and it reduces to an MQ subscribe problem.

cl=CoLink(addr,jwt)
key="".join(random.choices(string.ascii_letters + string.digits, k=188))
cl.subscribe(key, None)

This code throws an gRPC error:

"MQ Bind Error: protocol error: AMQP hard error: FRAME-ERROR: FRAME_ERROR - cannot decode

I discovered that with key length<=187 nothing happens, but with any key len>=188 the above error always occur.

[stneng]

#31