scons,ruby: do not generate unnecessary files

Do not generate garnet tester file or Ruby debug headers without a Ruby
protocol (i.e. PROTOCOL=None). It makes no sense to include these files
into the build when there will be no protocol to utilize them.

Change-Id: I8db4dd532f60008217a10c88a2e089f85df9d104
Reviewed-on: https://gem5-review.googlesource.com/8381
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

ruby: rename networktest to garnet_synthetic_traffic.
networktest is essentially a collection of synthetic traffic patterns
for the network. The protocol name and the tester having the same name
led to multiple python configuration files with the same name, adding
confusion. This patch renames networktest to garnet_synthetic_traffic,
and also adds more synthetic traffic patterns.