Removed unused import.

``cd`` was being imported but not being used.
Switched from yum-config-manager to sub-manager.

No longer installing `yum-config-manager` for ``Satellite 6`` installs
as it can take a while for YUM to re-fresh its cache. Instead, use
`subscription-manager repos` to first disable everything and then
enabled the RHEL repos we want. Note that since our custom `satellite`
repo is not a RHEL repo and is enabled by default, we do not have to
explicitly enable it anymore.

This should speed up the installs considerably.
Pass full path of device to `resize2fs`.
Merge pull request #8 from omaciel/fix-installer

Fix installer