cbuildbot: Switch from global site_config to local instance.

Remove the use of cbuildbot_config's global "GetConfig()" from
scripts/cbuildbot.py. This includes some interface changes that
required a number of other files to be modified as well.

In the process, several unittest were switch from using a production
SiteConfig to using Mock test values (good, especially in the long
run).

BUG=chromium:483566
TEST=lint + run_tests --network (this change is a little scary).
     cbuildbot --remote lumpy-paladin

Change-Id: Ibc308becf745da44b860e4f54718983a0f58defe
Reviewed-on: https://chromium-review.googlesource.com/274162
Reviewed-by: Sheng-liang Song <ssl@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
Commit-Queue: David James <davidjames@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/scripts/cbuildbot_unittest.py b/scripts/cbuildbot_unittest.py
index ed36881..177c9ee 100644
--- a/scripts/cbuildbot_unittest.py
+++ b/scripts/cbuildbot_unittest.py
@@ -6,6 +6,7 @@
 
 from __future__ import print_function
 
+from chromite.cbuildbot import config_lib_unittest
 from chromite.cbuildbot import constants
 from chromite.lib import cros_test_lib
 from chromite.scripts import cbuildbot
@@ -17,9 +18,11 @@
   # pylint: disable=W0212
   def testIsDistributedBuilder(self):
     """Tests for _IsDistributedBuilder() under various configurations."""
+    site_config = config_lib_unittest.MockSiteConfig()
+
     parser = cbuildbot._CreateParser()
     argv = ['x86-generic-paladin']
-    (options, _) = cbuildbot._ParseCommandLine(parser, argv)
+    (options, _) = cbuildbot._ParseCommandLine(parser, argv, site_config)
     options.buildbot = False
     options.pre_cq = False