Upgrade Maven Exec plugin to version 1.2.1

Release Notes - Maven 2.x Exec Plugin - Version 1.2.1

Bug

[MEXEC-80] -         exec:java squelches the first AWT exception
[MEXEC-88] -         ExecMojo: SuccessCodes config seems not to be recognized by commons exec framework
[MEXEC-89] -         Exceptions are not reported until program termination
[MEXEC-92] -         The plugin behaves unexpected when a file or a directory exist in the top level directory that has the same name as the given executable
[MEXEC-98] -         "object is not an instance of declaring class" error
[MEXEC-100] -       Plugin breaks arguments containing quotes

Improvement

[MEXEC-99] -         Use int[] instead of java.util.List for successCodes