Rename Runnable classes from Tasks to Actions

This is cleanup relating to a naming decision that we made awhile ago
but never got around to.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117244827

java/com/google/domain/registry/rde/JSchSshSession.java

@@ -40,7 +40,7 @@ import javax.inject.Inject;
  * as-needed basis.
  *
  * @see JSchSftpChannel
- * @see RdeUploadTask
+ * @see RdeUploadAction
  * @see com.jcraft.jsch.Session
  */
 final class JSchSshSession implements Closeable {