Update cbuildbot.py to upload prebuilts from preflight buildbot.

bin/cbuildbot_unittest.py

Index: bin/cbuildbot_unittest.py
diff --git a/bin/cbuildbot_unittest.py b/bin/cbuildbot_unittest.py
index 979cda55d40d2a258ce75a1c1f7ccd2706b0fe10..1353b7c36c5a2987de06accab4a557bea23fb2be 100755
--- a/bin/cbuildbot_unittest.py
+++ b/bin/cbuildbot_unittest.py
@@ -171,10 +171,13 @@ class CBuildBotTest(mox.MoxTestBase):
     m_file.read().AndReturn(self._test_string)
     m_file.close()
 
+    drop_file = '%s/src/scripts/cbuildbot_package.list' % self._buildroot
     cbuildbot.RunCommand(['./cros_mark_as_stable', '--all',
                      '--board=%s' % self._test_board,
                      '--overlays=%s' % ':'.join(self._chroot_overlays),
-                     '--tracking_branch=cros/master', 'commit'],
+                     '--tracking_branch=cros/master',
+                     '--drop_file=%s' % ReinterpretPathForChroot(drop_file),
+                     'commit'],
                      cwd='%s/src/scripts' % self._buildroot,
                      enter_chroot=True)
 
@@ -194,10 +197,13 @@ class CBuildBotTest(mox.MoxTestBase):
     m_file.read().AndReturn('None')
     m_file.close()
 
+    drop_file = '%s/src/scripts/cbuildbot_package.list' % self._buildroot
     cbuildbot.RunCommand(['./cros_mark_as_stable', '--all',
                          '--board=%s' % self._test_board,
                          '--overlays=%s' % ':'.join(self._chroot_overlays),
-                         '--tracking_branch=cros/master', 'commit'],
+                         '--tracking_branch=cros/master',
+                         '--drop_file=%s' % ReinterpretPathForChroot(drop_file),
+                         'commit'],
                          cwd='%s/src/scripts' % self._buildroot,
                          enter_chroot=True)