Define the bazel_metrics directory in $OUT.

$OUT/bazel_metrics directory is created in order to dump the
set of bazel profile files being created from a single build
execution. The directory is created from soong_ui.

Bug: b/173028918
Test: * m nothing and check out dir that there is no bazel_metrics dir.
      * USE_BAZEL=1 and checked out/bazel_metrics was created.
      * Ran m nothing and verified that out/bazel_metrics directory is
        deleted to ensure no metrics is uploaded or collected from the
	pipeline.

Change-Id: I1d3c2471065fae6931f35cef7f0f35fd84f76bef