crosperf: Print top5 commands into log

Enable top in nightly tests and print top 5 commands with high CPU usage
into log.

BUG=chromium:966514
TEST=unittests and HW tests on eve passed.

Change-Id: I0efd7f0875829c4423e998ec2fbec7436f7ae148
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/1829309
Tested-by: Denis Nikitin <denik@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
diff --git a/buildbot_test_toolchains.py b/buildbot_test_toolchains.py
index 6a72f3c..e289b1a 100755
--- a/buildbot_test_toolchains.py
+++ b/buildbot_test_toolchains.py
@@ -159,6 +159,7 @@
     cooldown_temp: 40
     cooldown_time: 10
     cpu_freq_pct: 95
+    top_interval: 1
     """ % (self._board, self._remotes)
     experiment_tests = """
     benchmark: all_toolchain_perf {