Add platform/system/update_engine to the manifest

BUG: 22357920
Change-Id: Ib3ff7d632126c45183ae6eaf3698459ff6a83935

default.xml

@@ -485,6 +485,7 @@
   <project path="system/media" name="platform/system/media" groups="pdk" />
   <project path="system/netd" name="platform/system/netd" groups="pdk" />
   <project path="system/security" name="platform/system/security" groups="pdk" />
+  <project path="system/update_engine" name="platform/system/update_engine" />
   <project path="system/vold" name="platform/system/vold" groups="pdk" />
   <project path="system/wifi" name="platform/system/wifi" />
   <project path="tools/adt/eclipse" name="platform/tools/adt/eclipse" groups="notdefault,tools" />