client: fix script execution

if __name__ == "__main__" should be first instead of try block. We want
execute it only when file was executed as script

https://fedorahosted.org/freeipa/ticket/6392

Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>

client/ipa-client-install

@@ -257,8 +257,9 @@ def main():
 
     return rval
 
-try:
+
 if __name__ == "__main__":
+    try:
         sys.exit(main())
     except KeyboardInterrupt:
         sys.exit(1)