The Unicode type is 'unicode' in Python 2 and 'str' on Python 3.
This patch replaces unicode with six.text_type to make Murano
more compatible with Python 3. Also it replaces the tuple
'(str, unicode)' with six.string_types for instance comparision.
Blueprint murano-python-3-support
Change-Id: I4db27afdb556ec30dd36d7d4e170055274edfa8b