Fix Neutron plugin XTRACE handling

The various Neutron plugin files need to have unique variables for the
xtrace state as they are sometimes nested more than two levels deep
and MY_XTRACE is getting stomped.  This gives each of the neutron_plugin
and neutron_thirdparty include files a unique XTRACE state variable.

I don't think this is a problem with any of the other plugin include
files (yet) so this just handles Neutron for now.

Change-Id: I7c272a48e7974edecaff5f431ff7443dd6622588
diff --git a/lib/neutron_thirdparty/vmware_nsx b/lib/neutron_thirdparty/vmware_nsx
index 3fecc62..7a76570 100644
--- a/lib/neutron_thirdparty/vmware_nsx
+++ b/lib/neutron_thirdparty/vmware_nsx
@@ -11,7 +11,7 @@
 # * NSX_GATEWAY_NETWORK_CIDR         --> CIDR to configure br-ex, e.g. 172.24.4.211/24
 
 # Save trace setting
-MY_XTRACE=$(set +o | grep xtrace)
+NSX3_XTRACE=$(set +o | grep xtrace)
 set +o xtrace
 
 # This is the interface that connects the Devstack instance
@@ -83,4 +83,4 @@
 }
 
 # Restore xtrace
-$MY_XTRACE
+$NSX3_XTRACE