skip soong tests by default for b command

It doesn't really make sense to incur the cost of running Soong tests to
Bazel users. We can shave off 20 seconds from the local critical path
during clean builds (or if Soong itself has changed) by enabling
--skip-soong-tests in the b command.

Test: b build '...'
Test: b build '...' --run-soong-tests
Bug: 240231596
Change-Id: I77d652502dc000908166e13045aa3e245c2e762c