Treat ClosedChannelException as UNAVAILABLE to squelch test failures
Treat ClosedChannelException as UNAVAILABLE to squelch test failures

Our tests are detecting cases where we are still getting
ClosedChannelException. We need to fix that because it is a useless
status, but until it is fixed we want a stable CI.

Fixes #1513 and NettyTransportTest.serverNotListening failures

rmichela/grpc-java,rmichela/grpc-java,rmichela/grpc-java,simonhorlick/grpc-java,carl-mastrangelo/grpc-java,elandau/grpc-java,dapengzhang0/grpc-java,nmittler/grpc-java,anuraaga/grpc-java,nmittler/grpc-java,LuminateWireless/grpc-java,louiscryan/grpc-java,ejona86/grpc-java,zhangkun83/grpc-java,stanley-cheung/grpc-java,elandau/grpc-java,LuminateWireless/grpc-java,zhangkun83/grpc-java,simonhorlick/grpc-java,carl-mastrangelo/grpc-java,pieterjanpintens/grpc-java,ejona86/grpc-java,simonhorlick/grpc-java,pieterjanpintens/grpc-java,pieterjanpintens/grpc-java,LuminateWireless/grpc-java,dapengzhang0/grpc-java,stanley-cheung/grpc-java,grpc/grpc-java,zpencer/grpc-java,zpencer/grpc-java,dapengzhang0/grpc-java,stanley-cheung/grpc-java,anuraaga/grpc-java,carl-mastrangelo/grpc-java,louiscryan/grpc-java,simonhorlick/grpc-java,dapengzhang0/grpc-java,zpencer/grpc-java,ejona86/grpc-java,rmichela/grpc-java,zhangkun83/grpc-java,stanley-cheung/grpc-java,louiscryan/grpc-java,nmittler/grpc-java,elandau/grpc-java,anuraaga/grpc-java,carl-mastrangelo/grpc-java,zhangkun83/grpc-java,grpc/grpc-java,zpencer/grpc-java,grpc/grpc-java,elandau/grpc-java,grpc/grpc-java,ejona86/grpc-java,pieterjanpintens/grpc-java