clientconn: buffer waitC on Dial goroutine

[heyitsanthony]

Leaks a goroutine on dial timeout if unbuffered.

/cc @xiang90

[xiang90]

@heyitsanthony This change looks good to me.

@iamqizhao By reading the code, I found another issue. So if we have multiple addresses, the routine will try to connect them one by one until succeeds. However the main routine will exit at the first error. This seems to be broken.

[iamqizhao]

LGTM

@xiang90 This spawned goroutine will also exit at the first error. Do I miss anything?

[xiang90]

@iamqizhao Should it exit at the first error? Or it should continue to try other address?

[iamqizhao]

@xiang90 For simplicity, I let it exit at the first error now. I agree it is debatable what is the best thing to do here. Probably it should be exit if all the connections.

[xiang90]

@iamqizhao ACK. Works for me.