Add Python style checker to system/bt

* Based on Google style and ensure 4 spaces are used for indentation
* http://google.github.io/styleguide/pyguide.html

Bug: 146016811
Test: upload CLs
Change-Id: I27b9232d59e9e9bd59ca1414ef6f9db85c41a808
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
index 380216c..a473040 100644
--- a/PREUPLOAD.cfg
+++ b/PREUPLOAD.cfg
@@ -6,4 +6,5 @@
 
 [Hook Scripts]
 aosp_first = ${REPO_ROOT}/frameworks/base/tools/aosp/aosp_sha.sh ${PREUPLOAD_COMMIT} ".*$"
+yapf_hook = ./tools/scripts/yapf_checker.py