…ity (#27380)

* [VAULT-27917] fix(enos): handle SLES guestregister.service unreliability

The SLES provided `guestregister.service` systemd unit is unreliable
enough that it will fail ~ 1/9 times when provisioning SLES instances.
When this happens the machine will never successfully exec SUSEConnect
to enroll and we'll get no access to the SLES repositories and
subsequently break our scenarios.

I resolved this by restructuring our `install_packages` module to to
separate repository synchronization, repository addition, and package
installation into different scripts and resources and by adding special
case handling for SLES and the `guestregister.service`.

I also make a distinction between `dnf` and `yum` because while they are
sort of the same thing on RHEL, it is not the case with Amazon2. I also
shimmed out the rest of the support for Apt in case we ever need to add
repos there.

* Revert "Temporarily remove SLES from samples (#27378)"

This reverts commit 490cdd9.

Signed-off-by: Ryan Cragun <[email protected]>

…estiges of Ubuntu 18.04 testing (#27416)

It appears that starting with v0.5.2 the misspell linter embeds the
version directory into the release archive.

Signed-off-by: Ryan Cragun <[email protected]>