1128831 - Restore python-rhsm-1.8.0.

Bring back python-rhsm-1.8.0 for CentOS users. This is the exact code
that was removed in ecdb3ed0[0].

[0] https://github.com/pulp/pulp/commit/ecdb3ed0d95f2fbaf5f5ec6363ecb3d82386d806

https://bugzilla.redhat.com/show_bug.cgi?id=1128831
Add dist_list.txt and README for python-rhsm.
Merge branch 'rbarlow-1128831' into pulp-2.4