Pin the version of graphene for python2
Pin the version of graphene for python2

After graphene 3.0 has been released, DLRN it's failing to install in
CentOS 7 and version is only compatible to python3. This review is
pinning the version of graphene to last 2.X for python2 systems.

Change-Id: I7ac9a9734e13b505ecfab9960318d1c6c0f1e01e

openstack-packages/delorean,openstack-packages/delorean