Make sure the nolog argument to ipautil.run is not a bare string

ipautil.run expects a tuple of passwords for nolog; passing a
single string causes all individual letters from that string to
be replaced by Xes.

This fixes such a call, and adds a sanity check to ipautil.run
that prevents lone strings from being used in nolog.

https://fedorahosted.org/freeipa/ticket/2419

ipaserver/install/krbinstance.py

@@ -305,7 +305,7 @@ class KrbInstance(service.Service):
             self.master_password + '\n',
         )
         try:
-            ipautil.run(args, nolog=(self.master_password), stdin=''.join(dialogue))
+            ipautil.run(args, nolog=(self.master_password,), stdin=''.join(dialogue))
         except ipautil.CalledProcessError, e:
             print "Failed to initialize the realm container"