python: more readable Ruby dot topology

python: more readable Ruby dot topology

Controllers may have the same name under different parents, thus
the controller full path is used as label. To avoid long and redundant
labels, common prefixes and suffixes are removed from the path.

Change-Id: Id793b59a4c38f3425ae5348138ae1d74c823edd7
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/41093
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>