Try to fix python3 compatibility ...

Work in progress ...

pwman/tests/test_tools.py

@@ -37,7 +37,8 @@ class DummyCallback3(Callback):
         return u'newsecret'
 
     def getsecret(self, question):
-        return u'12345'
+        ans = '12345'
+        return ans
 
     def getnewsecret(self, question):
         return u'newsecret'

pwman/util/crypto.py

@@ -426,6 +426,8 @@ class CryptoEngine(object):
         """
         retrieve encrypted data
         """
+        if sys.version_info.major > 2:
+            return plaintext
         try:
             plaintext.decode('utf-8')
         except UnicodeDecodeError: