sweet: make tile38 and go-build with -short even shorter

-short is not meant to be used for benchmarking; just for testing and

Change tile38 to run with a bare (empty) database, since a substantial
amount of time is spent on loading the database from disk. The lack of a
database also means that the tile38 server uses substantially less
memory, so we can let it run in parallel with more tasks in the
end-to-end test.

Change go-build to not do a first build of the target package during
Sweet's build step: it means the results won't be as useful since
they'll include downloading packages, but in -short mode it doesn't

Change-Id: I9e3559c4077fff696a374b97f91491783a26e5ac
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/506559
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
3 files changed