Fixes #60. Stop progress printing thread after upload

This is not the most elegant solution, but it does stop the progress printer
after the upload is done.

glacieruploader-command/src/main/java/de/kopis/glacier/commands/UploadArchiveCommand.java

@@ -36,10 +36,12 @@
 import java.math.MathContext;
 import java.util.List;
 import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 
 public class UploadArchiveCommand extends AbstractCommand {
 
+    public static final ScheduledExecutorService SCHEDULED_POOL = Executors.newScheduledThreadPool(1);
     public static final int PROGRESS_PRINT_PERIOD = 5;
     private final ArchiveTransferManager atm;
 
@@ -79,7 +81,7 @@ private BigDecimal calcPercentage(double x1, double y1) {
                     return x.divide(y, MathContext.DECIMAL64).multiply(BigDecimal.valueOf(100));
                 }
             };
-            Executors.newScheduledThreadPool(1).scheduleAtFixedRate(progressPrinter, 3, PROGRESS_PRINT_PERIOD, TimeUnit.SECONDS);
+            SCHEDULED_POOL.scheduleAtFixedRate(progressPrinter, 3, PROGRESS_PRINT_PERIOD, TimeUnit.SECONDS);
         }
         final String archiveId = atm.upload(sameAccountId, vaultName, uploadFile.getName(), uploadFile,
                 progressTracker).getArchiveId();
@@ -96,6 +98,9 @@ public void exec(OptionSet options, GlacierUploaderOptionParser optionParser) {
         for (File uploadFile : files) {
             this.upload(vaultName, uploadFile);
         }
+
+        // stop progress tracker
+        SCHEDULED_POOL.shutdown();
     }
 
     @Override