Fix UnicodeDecodeErrors with files containing non-ascii chars

The main issue here is a user trying to start deluge and the XDG
`user-dirs.dirs` file contains dir names with non-ascii chars causing
a UnicodeDecodeError when comparing with unicode chars since Py2
default encoding is ascii.

The solution is to use io.open as used elsewhere in code with
encoding set to utf8. Applied to all usage of open in common.

deluge/common.py

@@ -26,7 +26,7 @@ import tarfile
 import time
 from contextlib import closing
 from datetime import datetime
-from io import BytesIO
+from io import BytesIO, open
 
 import pkg_resources
 
@@ -147,7 +147,8 @@ def get_default_download_dir():
         from xdg.BaseDirectory import xdg_config_home
 
         try:
-            with open(os.path.join(xdg_config_home, 'user-dirs.dirs'), 'r') as _file:
+            user_dirs_path = os.path.join(xdg_config_home, 'user-dirs.dirs')
+            with open(user_dirs_path, 'r', encoding='utf8') as _file:
                 for line in _file:
                     if not line.startswith('#') and line.startswith('XDG_DOWNLOAD_DIR'):
                         download_dir = os.path.expandvars(
@@ -1141,7 +1142,7 @@ def create_auth_file():
     auth_file = deluge.configmanager.get_config_dir('auth')
     # Check for auth file and create if necessary
     if not os.path.exists(auth_file):
-        with open(auth_file, 'w') as _file:
+        with open(auth_file, 'w', encoding='utf8') as _file:
             _file.flush()
             os.fsync(_file.fileno())
         # Change the permissions on the file so only this user can read/write it
@@ -1157,7 +1158,7 @@ def create_localclient_account(append=False):
     if not os.path.exists(auth_file):
         create_auth_file()
 
-    with open(auth_file, 'a' if append else 'w') as _file:
+    with open(auth_file, 'a' if append else 'w', encoding='utf8') as _file:
         _file.write(
             ':'.join(
                 [
@@ -1186,7 +1187,7 @@ def get_localhost_auth():
 
         create_localclient_account()
 
-    with open(auth_file) as auth:
+    with open(auth_file, encoding='utf8') as auth:
         for line in auth:
             line = line.strip()
             if line.startswith('#') or not line: