Open metadata in binary mode for Python 3 compatibility.

Python 3 handles character data read from a file differently
than Python 2 does.

Python 3 opens files in text mode by default, causing file reads
to return string data decoded from file using encoding specified
as argument of open() builtin function.
If encoding is not specified, open() uses some default encoding
that can even be ASCII.

Hence, using open() in text mode without specifying encoding
is dangerous in Python 3 and can lead to unexpected results.

However, it's safe to open metadata in binary mode, it gets encoded
to UTF-8 later anyway.

Signed-off-by: Oleg Girko <ol@infoserver.lv>

src/saml2/mdstore.py

@@ -589,7 +589,7 @@ class MetaDataFile(InMemoryMetaData):
         self.cert = cert
 
     def get_metadata_content(self):
-        return open(self.filename).read()
+        return open(self.filename, 'rb').read()
 
     def load(self):
         _txt = self.get_metadata_content()