Add tracer to runBazel function.

Added a tracer named "bazel" in runBazel function to capture topline
metrics when running bazel.

Bug: b/173028918
Test: * USE_BAZEL=1 m nothing and checked soong_metrics file using
        printproto command to verify that bazel topline metrics
	were captured.
Change-Id: I5cb0728a4da48545dc701cc79627c318d5d9a29d