Fix dep exclusion: avro-ipc, not avro, depends on netty.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #763 from vanzin/netty-dep-hell and squashes the following commits:

dfb6ce2 [Marcelo Vanzin] Fix dep exclusion: avro-ipc, not avro, depends on netty.