infra_libs: explicitly import from third_party

We want to pull third_party out of implicit sys.path search,
so change importing of these modules to explicit.

BUG=b:187794934
TEST=CQ passes

Change-Id: I04cfcbe28930b8a04febad2cb192f2a8f5e3cd5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2917735
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/sysmon/osinfo_metrics_unittest.py b/scripts/sysmon/osinfo_metrics_unittest.py
index 148821f..66913b6 100644
--- a/scripts/sysmon/osinfo_metrics_unittest.py
+++ b/scripts/sysmon/osinfo_metrics_unittest.py
@@ -18,8 +18,9 @@
   """Tests for osinfo_metrics."""
 
   def setUp(self):
-    patcher = mock.patch('infra_libs.ts_mon.common.interface.state.store',
-                         autospec=True)
+    patcher = mock.patch(
+        'chromite.third_party.infra_libs.ts_mon.common.interface.state.store',
+        autospec=True)
     self.store = patcher.start()
     self.addCleanup(patcher.stop)