[autotest] Migrate graphite directory to client/common_lib/cros

This change allows us to report stats in client tests.
1. Change import paths for all files that import modules from graphite
2. Clean up some unused modules
Related CL: https://chromium-review.googlesource.com/#/c/202467/
BUG=chromium:237255
TEST=Ran scheduler locally, scheduled reboot jobs, verified stats such as monitor_db_cleanup.user_cleanup._cleanup were reported on chromeos-stats.
DEPLOY = apache, scheduler, host_scheduler
Change-Id: Iebfe3b8acc1c363a0b70ea555744e85d1367cb67
Reviewed-on: https://chromium-review.googlesource.com/202727
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Michael Liang <michaelliang@chromium.org>
Tested-by: Michael Liang <michaelliang@chromium.org>
diff --git a/scheduler/host_scheduler.py b/scheduler/host_scheduler.py
index 6009706..959c9d8 100755
--- a/scheduler/host_scheduler.py
+++ b/scheduler/host_scheduler.py
@@ -34,13 +34,13 @@
 from autotest_lib.frontend import setup_django_environment
 
 from autotest_lib.client.common_lib import global_config
+from autotest_lib.client.common_lib.cros.graphite import stats
 from autotest_lib.scheduler import email_manager
 from autotest_lib.scheduler import query_managers
 from autotest_lib.scheduler import rdb_lib
 from autotest_lib.scheduler import rdb_utils
 from autotest_lib.scheduler import scheduler_lib
 from autotest_lib.scheduler import scheduler_models
-from autotest_lib.site_utils.graphite import stats
 
 _db_manager = None
 _shutdown = False