Fix byte vs string file io for python 3

Reference: https://github.com/avocado-framework/avocado/issues/2024Signed-off-by: NJan Zerebecki <jan.foss@zerebecki.de>

selftests/unit/test_archive.py

@@ -27,7 +27,8 @@ class ArchiveTest(unittest.TestCase):
                 compressdir = self.compressdir
             str_length = self.sys_random.randint(30, 50)
             fd, filename = tempfile.mkstemp(dir=compressdir, text=True)
-            os.write(fd, data_factory.generate_random_string(str_length))
+            with os.fdopen(fd, 'w') as f:
+                f.write(data_factory.generate_random_string(str_length))
             relative_path = filename.replace(self.compressdir, '')
             hash_map_1[relative_path] = crypto.hash_file(filename)
 
@@ -47,7 +48,8 @@ class ArchiveTest(unittest.TestCase):
     def compress_and_check_file(self, extension):
         str_length = self.sys_random.randint(30, 50)
         fd, filename = tempfile.mkstemp(dir=self.basedir, text=True)
-        os.write(fd, data_factory.generate_random_string(str_length))
+        with os.fdopen(fd, 'w') as f:
+            f.write(data_factory.generate_random_string(str_length))
         original_hash = crypto.hash_file(filename)
         dstfile = filename + extension
         archive_filename = os.path.join(self.basedir, dstfile)