Add external/yapf to manifest

Bug: 111507925
Change-Id: Ife58a605846366f621ba161abe0406c4f16a5af2

default.xml

@@ -388,6 +388,7 @@
   <project path="external/xmlrpcpp" name="platform/external/xmlrpcpp" groups="pdk" />
   <project path="external/xmp_toolkit" name="platform/external/xmp_toolkit" groups="pdk" />
   <project path="external/xz-embedded" name="platform/external/xz-embedded" groups="pdk" />
+  <project path="external/yapf" name="platform/external/yapf" groups="vts,pdk" />
   <project path="external/zlib" name="platform/external/zlib" groups="pdk" />
   <project path="external/zopfli" name="platform/external/zopfli" groups="pdk" />
   <project path="external/zxing" name="platform/external/zxing" groups="pdk" />