add partprobing/partx calls on device when zapping

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
Merge pull request #208 from alfredodeza/8653

add partprobing/partx calls on device when zapping
Use proper rpm %dist postfix for rhel7 rpms
Add tests for rhel rpm dist detection
Merge pull request #209 from davidvossel/rhel7-fix2

fixes more issues with rhel7 support