Pin twine to python 2.7.x compat version

Change-Id: Icf29ef9414a4b7d16d2046e534000036c6aa95ea
diff --git a/packer/provision/basebuild.sh b/packer/provision/basebuild.sh
index 80e8fd3..87dc516 100644
--- a/packer/provision/basebuild.sh
+++ b/packer/provision/basebuild.sh
@@ -150,7 +150,7 @@
         robotframework-requests \
         robotframework-sshlibrary \
         tox \
-        twine \
+        twine==1.15.0 \
         virtualenv
         # end of pip install list