The testing package has its own bazel package (it has BUILD file) and
this is not part of the final artifact built with common:client rule.
However, because of wild card inclusion in Common.gwt.xml, the whole
tree is included in GWT module, when used from Eclipse in super dev mode
debug sessions. To avoid needing to add @GwtIncompatible to all files in
this package, exclude this package from GWT module source path in the GWT
module definition.
Change-Id: Ib36348084d59cc5e10f8dc5c7c627fc4e3323609
b51d8cd76d