Fix for bug in Python TLVWriter

-- Fixed a bug in the Python TLVWriter implementation caused all instances
of the class to use the same output buffer.

Author: Jay Logue

src/tools/factory-prov-tool/WeaveTLV.py

@@ -69,8 +69,8 @@
 
 class TLVWriter(object):
 
-    def __init__(self, encoding=bytearray(), implicitProfile=None):
-        self._encoding = encoding
+    def __init__(self, encoding=None, implicitProfile=None):
+        self._encoding = encoding if encoding is not None else bytearray()
         self._implicitProfile = implicitProfile
         self._containerStack = []