Revert "Remove python/futures"

This reverts commit 834b414d19a34b1af2db8049803df0c75df70b29.

Reason for revert: Some VTS script still rely on this package.

Bug: 208308581
Change-Id: I0cd068d61612f23aa16a2b45f2fb0939e128f4bc
diff --git a/default.xml b/default.xml
index a7a6904..475cbd5 100644
--- a/default.xml
+++ b/default.xml
@@ -409,6 +409,7 @@
   <project path="external/python/dateutil" name="platform/external/python/dateutil" groups="pdk" />
   <project path="external/python/enum34" name="platform/external/python/enum34" groups="vts,pdk" />
   <project path="external/python/funcsigs" name="platform/external/python/funcsigs" groups="pdk" />
+  <project path="external/python/futures" name="platform/external/python/futures" groups="vts,pdk" />
   <project path="external/python/google-api-python-client" name="platform/external/python/google-api-python-client" groups="vts,pdk" />
   <project path="external/python/httplib2" name="platform/external/python/httplib2" groups="vts,pdk" />
   <project path="external/python/ipaddress" name="platform/external/python/ipaddress" groups="pdk" />