[update-checkout] Move all files except the top level entrypoints into ./utils/update_checkout/*.

This makes update_checkout into a true python module that we can add nosetests
for, readme, and also split up without issue into multiple small files.

I also added a small stub test directory and support for running tests for
update_checkout during validation-testing. So once we add some tests, everything
is setup correctly in terms of the swift build for testing purposes.

Author: gottesmm

utils/update_checkout/__init__.py

@@ -0,0 +1,4 @@
+
+from update_checkout import main
+
+__all__ = ["main"]

utils/update_checkout/tests/__init__.py

@@ -0,0 +1,4 @@
+
+from update_checkout import main
+
+__all__ = ["main"]

utils/update-checkout-config.json renamed to utils/update_checkout/update-checkout-config.json

@@ -414,7 +414,8 @@ def main():
         action='store_true')
     parser.add_argument(
         "--config",
-        default=os.path.join(SCRIPT_DIR, "update-checkout-config.json"),
+        default=os.path.join(SCRIPT_DIR, os.pardir,
+                             "update-checkout-config.json"),
         help="Configuration file to use")
     parser.add_argument(
         "--github-comment",
@@ -518,7 +519,3 @@ def main():
     else:
         print("update-checkout succeeded")
     sys.exit(fail_count)
-
-
-if __name__ == "__main__":
-    main()

utils/update_checkout/update_checkout/__init__.py

@@ -0,0 +1 @@
+// RUN: %{python} -m unittest discover -s %swift_src_root/utils/update_checkout