Add postgresql dev package as testonly neutron dep

The neutron functional job needs to build psycopg2 which has a
dependency on postgresql dev packages.

Change-Id: Ie5c8e2bd02e148d6638f4a4c1fbf6667c30313d5
diff --git a/files/rpms/neutron b/files/rpms/neutron
index 59152d6..d11dab7 100644
--- a/files/rpms/neutron
+++ b/files/rpms/neutron
@@ -9,6 +9,7 @@
 mysql-devel  # testonly
 mysql-server # NOPRIME
 openvswitch # NOPRIME
+postgresql-devel        # testonly
 python-eventlet
 python-greenlet
 python-iso8601