releasetools: Make blockimgdiff Python 3 compatible.

Bug: 131631303
Test: `python -m unittest test_blockimgdiff`
Test: `python3 -m unittest test_blockimgdiff`
Change-Id: I8cf072ca4af6a525bc675cba0be998ff7be7f4f1
diff --git a/tools/releasetools/test_blockimgdiff.py b/tools/releasetools/test_blockimgdiff.py
index b6d47d4..4c86933 100644
--- a/tools/releasetools/test_blockimgdiff.py
+++ b/tools/releasetools/test_blockimgdiff.py
@@ -268,6 +268,7 @@
 
 
 class DataImageTest(ReleaseToolsTestCase):
+
   def test_read_range_set(self):
     data = "file" + ('\0' * 4092)
     image = DataImage(data)
@@ -275,10 +276,11 @@
 
 
 class FileImageTest(ReleaseToolsTestCase):
+
   def setUp(self):
     self.file_path = common.MakeTempFile()
     self.data = os.urandom(4096 * 4)
-    with open(self.file_path, 'w') as f:
+    with open(self.file_path, 'wb') as f:
       f.write(self.data)
     self.file = FileImage(self.file_path)
 
@@ -292,18 +294,18 @@
         expected_data = self.data[s * blocksize : e * blocksize]
 
         rs = RangeSet([s, e])
-        data = "".join(self.file.ReadRangeSet(rs))
+        data = b''.join(self.file.ReadRangeSet(rs))
         self.assertEqual(expected_data, data)
 
         sha1sum = self.file.RangeSha1(rs)
         self.assertEqual(sha1(expected_data).hexdigest(), sha1sum)
 
         tmpfile = common.MakeTempFile()
-        with open(tmpfile, 'w') as f:
+        with open(tmpfile, 'wb') as f:
           self.file.WriteRangeDataToFd(rs, f)
-        with open(tmpfile, 'r') as f:
+        with open(tmpfile, 'rb') as f:
           self.assertEqual(expected_data, f.read())
 
   def test_read_all(self):
-    data = "".join(self.file.ReadRangeSet(self.file.care_map))
+    data = b''.join(self.file.ReadRangeSet(self.file.care_map))
     self.assertEqual(self.data, data)