Catch Exception instead of IOException.

Closes #22.

* src/dctc/java/com/dataiku/dctc/copy/CopyTaskRunnable.java: Here.
Clean the error message.

* src/dctc/java/com/dataiku/dctc/copy/CopyTasksExecutor.java: Here.
If an error appends while the transfer, set the exit code to 2.

* src/dctc/java/com/dataiku/dctc/command/Cp.java,
  src/dctc/java/com/dataiku/dctc/command/Mv.java,
  src/dctc/java/com/dataiku/dctc/command/Sync.java: Here.