android: Make benchmark string changes more random

Use a random int in the string replacement for benchmarks. This ensures
a unique run to get consistent caching and remote execution
measurements.

Previous attempts to avoid the remote cache did not produce consistent
results, since remote actions still cached nondeterministically on the
remote side. So we were able to turn off caching the entire action but
some aspects of it were still cached when the action ran remotely.
Rather than turning off remote execution entirely (which would not
produce accurate estimates of actual dev experience), make the benchmark
actions more unique instead.

Bug: 391348954
Change-Id: Ie0236ed96e8718213bd71826a41e73d861120ae4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6192050
Auto-Submit: Peter Wen <wnwen@chromium.org>
Commit-Queue: Peter Wen <wnwen@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1409949}