update the changelog

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
Support install on rhel7
add a test to make sure rhel7 support does not break

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
1.5.6
Use proper rpm %dist postfix for rhel7 rpms
Add tests for rhel rpm dist detection