Sanitizes log message input (#479)

* Sanitizes log message input

Fixes issue #478 in which invalid utf-8 characters that appeared in test
output were causing unhandled exceptions to be raised. The fix uses
built-in sanitization features to replace invalid characters with '?'.

* Fixes Python2/3 queue import error in test code

* Fixes unknown 'to_bytes' unittest for Python2

catkin_tools/execution/io.py

@@ -128,7 +128,7 @@ def _decode(self, data):
         """Decode bytes into Python str.
         :type data: bytes
         """
-        return data.decode('utf-8')
+        return data.decode('utf-8', 'replace')
 
     def __del__(self):
         if self.is_open:

tests/unit/test_io.py

@@ -0,0 +1,18 @@
+try:
+    # Python3
+    from queue import Queue
+except ImportError:
+    # Python2
+    from Queue import Queue
+
+import binascii
+from catkin_tools.execution import io as io
+
+
+def test_invalid_utf8_characters():
+    io_container = io.IOBufferContainer('test', 'test_id', 'test', Queue(), '/tmp')
+    bad_byte_array = binascii.a2b_hex(b'80')
+    try:
+        io_container._decode(bad_byte_array)
+    except UnicodeDecodeError:
+        assert False, "Bad decoding"