Display human readable bytes in download progress

Before:

```
Fetching https://mirror.bazel.build/..._x64.tar.gz; 28,324,614B 9s
```

After:

```
Fetching https://mirror.bazel.build/..._x64.tar.gz; 27 MB (28,324,614B) 9s
```

src/main/java/com/google/devtools/build/lib/bazel/repository/downloader/BUILD

@@ -30,5 +30,6 @@ java_library(
         "//third_party:auto_value",
         "//third_party:guava",
         "//third_party:jsr305",
+        "//third_party:apache_commons_io",
     ],
 )

src/main/java/com/google/devtools/build/lib/bazel/repository/downloader/DownloadProgressEvent.java

@@ -16,8 +16,8 @@
 
 import com.google.devtools.build.lib.events.ExtendedEventHandler;
 import java.net.URL;
-import java.text.NumberFormat;
 import java.util.Locale;
+import org.apache.commons.io.FileUtils;
 
 /**
  * Postable event reporting on progress made downloading an URL. It can be used to report the URL
@@ -73,9 +73,7 @@ public long getBytesRead() {
   @Override
   public String getProgress() {
     if (bytesRead > 0) {
-      NumberFormat formatter = NumberFormat.getIntegerInstance(Locale.ENGLISH);
-      formatter.setGroupingUsed(true);
-      return formatter.format(bytesRead) + "B";
+      return String.format("%s (%,dB)", FileUtils.byteCountToDisplaySize(bytesRead), bytesRead);
     } else {
       return "";
     }