Debump netty version by 1 due to ObjectCleaner bug (#1163)
Debump netty version by 1 due to ObjectCleaner bug (#1163)

The ObjectCleaner can possibly keep a process alive forever with netty
4.1.20 since it is not a daemon thread.

See: https://github.com/netty/netty/issues/7617

This causes initialize-cluster-metadata to hang forever. 4.1.19
doesn't have this issue, so we should drop down to that until the fix
is in a release.
ArvinDevel/incubator-pulsar,massakam/pulsar,massakam/pulsar,saandrews/pulsar,yahoo/pulsar,saandrews/pulsar,sschepens/pulsar,merlimat/pulsar,sschepens/pulsar,yahoo/pulsar,massakam/pulsar,ArvinDevel/incubator-pulsar,nkurihar/pulsar,nkurihar/pulsar,jai1/pulsar,jai1/pulsar,saandrews/pulsar,ArvinDevel/incubator-pulsar,saandrews/pulsar,jai1/pulsar,sschepens/pulsar,jai1/pulsar,merlimat/pulsar,nkurihar/pulsar,sschepens/pulsar,yahoo/pulsar,ArvinDevel/incubator-pulsar,saandrews/pulsar,saandrews/pulsar,jai1/pulsar,massakam/pulsar,ArvinDevel/incubator-pulsar,merlimat/pulsar,yahoo/pulsar,sschepens/pulsar,merlimat/pulsar,ArvinDevel/incubator-pulsar,sschepens/pulsar,saandrews/pulsar,jai1/pulsar,ArvinDevel/incubator-pulsar,ArvinDevel/incubator-pulsar,sschepens/pulsar,massakam/pulsar,jai1/pulsar,yahoo/pulsar,yahoo/pulsar,nkurihar/pulsar,nkurihar/pulsar,merlimat/pulsar,massakam/pulsar,sschepens/pulsar,nkurihar/pulsar,jai1/pulsar,jai1/pulsar,nkurihar/pulsar,saandrews/pulsar,merlimat/pulsar,nkurihar/pulsar,nkurihar/pulsar