Rename the dir for SystemUpdaterSample.

Also replace the occurrence in README.md and PREUPLOAD.cfg.

Test: mmma -j bootable/recovery
Change-Id: I04c0ef00dd64f49e008ad2a4a2c1e8eaed76bf8d
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
index 878651c..1084291 100644
--- a/PREUPLOAD.cfg
+++ b/PREUPLOAD.cfg
@@ -7,5 +7,5 @@
 
 [Hook Scripts]
 checkstyle_hook = ${REPO_ROOT}/prebuilts/checkstyle/checkstyle.py --sha ${PREUPLOAD_COMMIT}
-                  -fw sample_updater/
+                  -fw updater_sample/