TT#18774 Fix library get_nodename for Carrier case

Nodename is always 'sp1' or 'sp2' for both PRO and Carrier,
while none of them are available into Carrier's network.yml.
We should not destroy proper nodename in 'out' on Carrier
(in CE failover code). Ensure we are on CE before using 'self'.

P.S CE network.yml uses 'hosts.self' historically as we never
controlled the server filename on CE.

Change-Id: I6042511e8383a01b1439323204284cfb087e7bca

lib/get_nodename

@@ -17,7 +17,7 @@
 [% END -%]
 [%-
 
-IF !hosts.${out}.defined;
+IF hosts.self.defined && !hosts.${out}.defined;
   out = 'self';
 END;