It is not testing what it's supposed to be, I think. Try applying this patch and the test fails:

— a/jstests/replsets/replsethostnametrim.js
+++ b/jstests/replsets/replsethostnametrim.js
@@ -4,7 +4,7 @@ var replTest = new ReplSetTest(

);
var nodes = replTest.startSet();
replTest.initiate();

-var master = replTest.nodes[0];
+var master = replTest.getMaster();
var config = master.getDB("local").system.replset.findOne();
config.version++;
var origHost = config.members[0].host;

It is only working because reconfig returns 0 if the set isn't ready yet.