Update path of tradefederation projects.

project: platform/tools/tradefederation
original path: tools/tradefederation
new path:      tools/tradefederation/core
BUG:36557513
Test: Synced and built on aosp master with success.
- make -j40
- make -j49 javac-check dist DIST_DIR=<local dir> RUN_ERROR_PRONE=true

default.xml

@@ -571,7 +571,7 @@
   <project path="tools/studio/cloud" name="platform/tools/studio/cloud" groups="notdefault,tools" />
   <project path="tools/swt" name="platform/tools/swt" groups="notdefault,tools" />
   <project path="tools/test/connectivity" name="platform/tools/test/connectivity" groups="pdk" />
-  <project path="tools/tradefederation" name="platform/tools/tradefederation" groups="pdk,tradefed" />
+  <project path="tools/tradefederation/core" name="platform/tools/tradefederation" groups="pdk,tradefed" />
 
   <repo-hooks in-project="platform/tools/repohooks" enabled-list="pre-upload" />