Fix issue with Debian package checksums changing with each build

[WadeBarnes]

The checksums of the indy-plenum Debian packages change with each build, even when there are no code changes. If the code does not change, the checksum of the package should be the same each time it's built.

The biggest contributor to this issue is fpm (the tool used to build the packages). It includes a dummy changelog that has date and time stamps in it that change with each build.

The other contributors are the order of the content in the PKG-INFO and __manifest__.json files. Changes have recently been made to keep the contents of __manifest__.json ordered. However the tests_require section in setup.py still creates an unordered list that can change the order of the content in PKG-INFO from build to build.