releasetools: Make additional modules Python 3 compatible.

Bug: 131631303
Test: `python -m unittest test_sign_target_files_apks`
Test: `python3 -m unittest test_sign_target_files_apks`
Test: `python -m unittest test_add_img_to_target_files`
Test: `python3 -m unittest test_add_img_to_target_files`
Test: `python -m unittest test_ota_from_target_files`
Test: `python3 -m unittest test_ota_from_target_files`
Test: `python -m unittest test_validate_target_files`
Test: `python3 -m unittest test_validate_target_files`
Test: Run `python3 ota_from_target_files.py` to generate an OTA.
Test: Run `python3 sign_target_files_apks.py` to sign a target_files.
Change-Id: I56b45bbcbf7aa83e690785a9640c0212e45d12d8
diff --git a/tools/releasetools/test_sign_target_files_apks.py b/tools/releasetools/test_sign_target_files_apks.py
index e142ebb..9a1d163 100644
--- a/tools/releasetools/test_sign_target_files_apks.py
+++ b/tools/releasetools/test_sign_target_files_apks.py
@@ -136,7 +136,7 @@
       ReplaceVerityKeyId(input_zip, output_zip, cert_file)
 
     with zipfile.ZipFile(output_file) as output_zip:
-      self.assertEqual(BOOT_CMDLINE1, output_zip.read('BOOT/cmdline'))
+      self.assertEqual(BOOT_CMDLINE1, output_zip.read('BOOT/cmdline').decode())
 
     # Test with the second certificate.
     cert_file = os.path.join(self.testdata_dir, 'testkey.x509.pem')
@@ -146,7 +146,7 @@
       ReplaceVerityKeyId(input_zip, output_zip, cert_file)
 
     with zipfile.ZipFile(output_file) as output_zip:
-      self.assertEqual(BOOT_CMDLINE2, output_zip.read('BOOT/cmdline'))
+      self.assertEqual(BOOT_CMDLINE2, output_zip.read('BOOT/cmdline').decode())
 
   def test_ReplaceVerityKeyId_no_veritykeyid(self):
     BOOT_CMDLINE = (
@@ -164,7 +164,7 @@
       ReplaceVerityKeyId(input_zip, output_zip, None)
 
     with zipfile.ZipFile(output_file) as output_zip:
-      self.assertEqual(BOOT_CMDLINE, output_zip.read('BOOT/cmdline'))
+      self.assertEqual(BOOT_CMDLINE, output_zip.read('BOOT/cmdline').decode())
 
   def test_ReplaceCerts(self):
     cert1_path = os.path.join(self.testdata_dir, 'platform.x509.pem')