[Bitbucket] error_msg concatenation error in raise_for_status fix and python 2 support

[Viktxrrr]

I noticed that there is a need to support Python 2 - #1453.
Maybe then we should change the fix #1493 to something like this?

error_msg += "\n" + str(e["detail"])

[Viktxrrr]

Then I also have to delete trailing comma here - https://github.com/atlassian-api/atlassian-python-api/blob/master/atlassian/rest_client.py#L76

[gonchik]

@Viktxrrr sure, let's do it :)

[gonchik]

3.41.19 published and fixed