Add "Running ... " output to nomulus tool confirming commands

This makes it more clear than an operation is actually pending, rather
than nothing changing after pressing "Y" to run the command.

The prompt now looks like when you press "Y" and "N", respectively:

Perform this command? (y/N): Running ...

Perform this command? (y/N): Command aborted.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=193521084

java/google/registry/tools/ConfirmingCommand.java

@@ -37,6 +37,7 @@ public abstract class ConfirmingCommand implements Command {
         // nothing further.
         return;
       } else if (force || promptForYes("Perform this command?")) {
+        System.out.println("Running ... ");
         System.out.println(execute());
         printLineIfNotEmpty(postExecute());
       } else {