dashboard: use sharded test helpers for freebsd-386-gce101
dashboard: use sharded test helpers for freebsd-386-gce101

It's a trybot, but was only using a single machine, making it the long
tail and slowing down trybot results.

Change-Id: I09ccc56b3866d522e4abf96215a2e293aed4e4d6
Reviewed-on: https://go-review.googlesource.com/14954
Reviewed-by: David Crawshaw <a2f0bf29257797dd66800b4fbb9945c3e216c004@golang.org>

golang/build,golang/build,golang/build,golang/build,proppy/build,proppy/build,proppy/build,proppy/build