Work around slow upload speed caused by httplib hardcoded small blocksize

disk.py

@@ -323,23 +323,34 @@ class Disk(object):
         subprocess.check_output(cmdline)
         size = os.path.getsize(exported_path)
 
+        percent = [0]
+
         def update_state(monitor):
-            percent = monitor.bytes_read * 100 / size
+            new_percent = monitor.bytes_read * 100 / size
             if task.is_aborted():
                 raise AbortException()
-            task.update_state(
-                task_id=parent_id,
-                state=task.AsyncResult(parent_id).state,
-                meta={'percent': percent}
-            )
+            if new_percent > percent[0]:
+                percent[0] = new_percent
+                task.update_state(
+                    task_id=parent_id,
+                    state=task.AsyncResult(parent_id).state,
+                    meta={'percent': percent[0]}
+                )
 
         with open(exported_path, 'rb') as exported_disk:
             try:
                 e = MultipartEncoder(
                     {'data': (exported_name + '.' + disk_format,
-                              exported_disk)}
+                              exported_disk,
+                              'application/octet-stream')}
                 )
                 m = MultipartEncoderMonitor(e, update_state)
+                # Force the read function to read more than 8192 bytes,
+                # which is a hardcoded value in httplib. This increases
+                # the upload speed. See:
+                # https://github.com/requests/toolbelt/issues/75
+                m._read = m.read
+                m.read = lambda _: m._read(1024 * 1024)
                 response = requests.post(
                     upload_link,
                     data=m,