siso: export more detailed completion statuses

Update reclientutil CompletionStatus and Siso build stats to
differentiate completion statuses:
- STATUS_CACHE_HIT_EARLY: actions completed due to early cache hit
  before any race
- STATUS_CACHE_HIT_LATE: actions where racing remote execution hit cache
  after race started
- STATUS_CACHE_HIT: total actions completed via cache hit (early or
  late)
- STATUS_RACING_REMOTE: actions where remote won (including
  STATUS_CACHE_HIT_LATE)
- STATUS_RACING_LOCAL: actions where local won

Also fix float division for build_cache_hit_ratio in RBEBuildMetrics.

TAG=agy
CONV=3a855756-465c-4db8-958f-89d1845363bd

Change-Id: I6533086b41a1f9b32fadd46ab3bc995a8a060386
Reviewed-on: https://chromium-review.googlesource.com/c/build/+/8177225
Reviewed-by: Junji Watanabe <jwata@google.com>
Reviewed-by: Alex Ovsienko <ovsienko@google.com>
Commit-Queue: LaMont Jones <lamontjones@chromium.org>