Fix Python3 test errors

This patch is fixing few errors related to Python3 and tests:

* Add the attribute "message" to the exception because it doesn't exist
  by default.

* Add the py35 runtime to tox.ini since we now run tests on Python3.5

* Drop the spec=file syntax because "file" is not a builtin type for
  Python3.

Change-Id: I31d1a5719d605974912bc26f65b96734631691d5
Closes-Bug: #1647337

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 minversion = 1.8
 skipsdist = True
-envlist = py34,py27,pep8
+envlist = py35,py34,py27,pep8
 
 [testenv]
 usedevelop = True

virtualbmc/exception.py

@@ -12,6 +12,7 @@
 
 
 class VirtualBMCError(Exception):
+    message = None
 
     def __init__(self, message=None, **kwargs):
         if self.message and kwargs:

virtualbmc/tests/unit/test_manager.py

@@ -86,7 +86,7 @@ class VirtualBMCManagerTestCase(base.TestCase):
     def _test__show(self, mock__parse, mock_pid, mock_open, expected=None):
         mock_pid.return_value = True
         mock__parse.return_value = self.domain0
-        f = mock.MagicMock(spec=file)
+        f = mock.MagicMock()
         f.read.return_value = self.domain0['port']
         mock_open.return_value.__enter__.return_value = f
 
@@ -212,7 +212,7 @@ class VirtualBMCManagerTestCase(base.TestCase):
     @mock.patch.object(os.path, 'exists')
     def test_stop(self, mock_exists, mock_remove, mock_kill, mock_open):
         mock_exists.return_value = True
-        f = mock.MagicMock(spec=file)
+        f = mock.MagicMock()
         f.read.return_value = self.domain0['port']
         mock_open.return_value.__enter__.return_value = f
 
@@ -234,7 +234,7 @@ class VirtualBMCManagerTestCase(base.TestCase):
     @mock.patch.object(os.path, 'exists')
     def test_stop_pid_file_not_found(self, mock_exists, mock_open):
         mock_exists.return_value = True
-        f = mock.MagicMock(spec=file)
+        f = mock.MagicMock()
         f.read.return_value = self.domain0['port']
         mock_open.return_value.__enter__.side_effect = IOError('boom')