Python update progress

[IsaacCalligeros95]

Original PR from community member @smlng. For Teamcity and security protocols in place this has to be re-created.

According to the documentation the message for updateprogress in Python scripts is optional. However, when a message is not provided the script fails because the default for message is None which is then passed to the inner encode() function that does not like None.

In this fix the default value for message is changed from None to "" (empty string). Further this PR provided necessary test fixtures to assert the correct behavior.