Add minimum version requirement for six

Salt uses the function add_metaclass function which had a different name
prior to six version 1.4.0.

Signed-off-by: Skyler Berg <skyler.berg@huawei.com>
Merge branch 'six-version-requirement' of https://github.com/skylerberg/salt into skylerberg-six-version-requirement
remove six dep, we bundle it now
Merge pull request #19141 from thatch45/skylerberg-six-version-requirement

Merge #19101 with fixes