Explicitly read setup.cfg as utf-8 on Python 3

Per the referenced bug, relying on the terminal encoding to read
setup.cfg is not safe.  Unfortunately, Python 2 doesn't accept an
encoding when reading config files so we need a fallback path for
that version.

Change-Id: If49344db2f9139c0557f6acd17671163e02468a5
Closes-Bug: 1745396

doc/source/user/using.rst

@@ -119,6 +119,11 @@ such as the ``extract_mesages`` section provided by Babel__.
            # A comment on a dedicated line
            value3
 
+.. note::
+
+   On Python 3 ``setup.cfg`` is explicitly read as UTF-8.  On Python 2 the
+   encoding is dependent on the terminal encoding.
+
 __ http://setuptools.readthedocs.io/en/latest/setuptools.html#configuring-setup-using-setup-cfg-files
 __ http://babel.pocoo.org/en/latest/setup.html
 

pbr/util.py

@@ -214,7 +214,11 @@ def cfg_to_args(path='setup.cfg', script_args=()):
     if not os.path.exists(path):
         raise errors.DistutilsFileError("file '%s' does not exist" %
                                         os.path.abspath(path))
-    parser.read(path)
+    try:
+        parser.read(path, encoding='utf-8')
+    except TypeError:
+        # Python 2 doesn't accept the encoding kwarg
+        parser.read(path)
     config = {}
     for section in parser.sections():
         config[section] = dict()