Fix lower-constraints and neutronclient-functional job

Change decorator in l-c.txt from 3.4.0 to 4.1.0
add neutron as devstack plugin to neutronclient-functional job.

Change-Id: Ib4b98f4e9e70f058ba5c7c43f559ab888edf1a88

.zuul.yaml

@@ -64,6 +64,7 @@
         Q_ML2_TENANT_NETWORK_TYPE: vxlan
         Q_ML2_PLUGIN_MECHANISM_DRIVERS: openvswitch
       devstack_plugins:
+        neutron: https://opendev.org/openstack/neutron
         neutron-vpnaas: https://opendev.org/openstack/neutron-vpnaas
 
 - job:

lower-constraints.txt

@@ -11,7 +11,7 @@ contextlib2==0.4.0
 coverage==4.0
 cryptography==2.7
 debtcollector==1.2.0
-decorator==3.4.0
+decorator==4.1.0
 deprecation==1.0
 docutils==0.11
 dogpile.cache==0.6.5