LoadBalancer.requestConnection() may be ignored if it's called before subchannels are created

[zhangkun83]

What version of gRPC-Java are you using?

v1.32.1

What did you expect to see?

Calling ManagedChannel.getState(true) will make the channel to try to connect to the server at least once, no matter when it's called.

What did you see instead?

Calling ManagedChannel.getState(true) makes the channel try to connect to server only if it's called after subchannels are created, i.e., after name resolution in pick-first, and after backend addresses are received in grpclb. If getState(true) is called before that point, the channel won't try to connect to servers after subchannels are created, unless getState(true) is called again.

/cc @ejona86