CORD-1426: Use release version of plyprotobuf

This is a bug fix. We currently pull the latest version of plyprotobuf,
whatever that might be. This patch sets the version to a constant, to
avoid breakages related to updates to the package in the future.

Change-Id: I7a42909b50b253cd68c849bf81222888e38ec32b
diff --git a/containers/xos/Dockerfile.corebuilder b/containers/xos/Dockerfile.corebuilder
index 6b364b7..1ac9e8b 100644
--- a/containers/xos/Dockerfile.corebuilder
+++ b/containers/xos/Dockerfile.corebuilder
@@ -6,7 +6,7 @@
 ADD xos/tosca/custom_types /opt/xos/tools/corebuilder/custom_types
 
 # Temporary fix. This should go away when we update xos-core to a more recent image.
-RUN pip install git+https://github.com/sb98052/plyprotobuf
+RUN pip install git+https://github.com/sb98052/plyprotobuf@v1.2.0
 
 ENV HOME /root
 WORKDIR /opt/xos/tools/corebuilder
@@ -30,3 +30,4 @@
 
 ENTRYPOINT ["/usr/bin/python", "corebuilder.py"]
 
+
diff --git a/containers/xos/pip_requirements.txt b/containers/xos/pip_requirements.txt
index b47ae86..4de76c6 100644
--- a/containers/xos/pip_requirements.txt
+++ b/containers/xos/pip_requirements.txt
@@ -155,4 +155,4 @@
 wsgiref==0.1.2
 zope.interface==4.3.3
 redis==2.10.5
-git+https://github.com/sb98052/plyprotobuf
+git+https://github.com/sb98052/plyprotobuf@v1.2.0