volumeupload: Use 1MiB read size

Rather than 1K. This drastically speeds up the volumeupload case
for a local URI for the cost of some higher runtime memory but
I think that's worth it

Fixes: #221

Signed-off-by: Cole Robinson <crobinso@redhat.com>

virtinst/install/volumeupload.py

@@ -108,8 +108,7 @@ def _upload_file(conn, meter, destpool, src):
         meter.start(size=size,
                     text=_("Transferring %s") % os.path.basename(src))
         while True:
-            # blocksize = (1024 ** 2)
-            blocksize = 1024
+            blocksize = 1024 * 1024  # 1 MiB
             data = fileobj.read(blocksize)
             if not data:
                 break