add python-enum34 for vrouter-netns

eventlet needs it but doesn't have in its dependencies

Change-Id: Iab97b7f595edcc798478383575d0972edbb7bb64
Closes-Bug: #1783519

rpm/contrail/contrail.spec

@@ -588,6 +588,7 @@ Requires:           python-unittest2
 Requires:           iproute >= 3.1.0
 Requires:           python-requests >= 2.5.1
 Requires:           python-eventlet
+Requires:           python-enum34
 Requires:           python-keystoneclient
 Requires:           python-barbicanclient
 Requires:           python-pyOpenSSL