Open config file in non-bytes mode

Nothing written into it is encoded, so it makes little sense, but it
does break in python3 the way it was before.

The variable names were adjusted to be less misleading.

Signed-off-by: Adrian Tschira <nota@notafile.com>

synapse/config/_base.py

@@ -281,15 +281,15 @@ class Config(object):
                     )
                 if not cls.path_exists(config_dir_path):
                     os.makedirs(config_dir_path)
-                with open(config_path, "wb") as config_file:
-                    config_bytes, config = obj.generate_config(
+                with open(config_path, "w") as config_file:
+                    config_str, config = obj.generate_config(
                         config_dir_path=config_dir_path,
                         server_name=server_name,
                         report_stats=(config_args.report_stats == "yes"),
                         is_generating_file=True
                     )
                     obj.invoke_all("generate_files", config)
-                    config_file.write(config_bytes)
+                    config_file.write(config_str)
                 print((
                     "A config file has been generated in %r for server name"
                     " %r with corresponding SSL keys and self-signed"