Use the `retry_options` on Gentoo, similar to how its already being used
across the state files for FreeBSD, since we're getting failures such as
this one:

* https://gitlab.com/myii/salt-formula/-/jobs/2285180374

Use the `retry_options` already being used for the Salt minion service,
since we're getting failures such as this one:

* https://github.com/myii/salt-formula/runs/2415072504

This is made worse by the fact that GitHub Actions cannot re-run a
single job (at the current time).

```bash
Examining salt/syndic.sls of type state
[201] Trailing whitespace
salt/syndic.sls:12
  {%- endif %}
```

The syndic service was depending upon itself, which caused the salt run
to fail. This commit fixes that by depending on the salt-master service
rather than the salt-syndic service. I also made it more general by
using IDs to specify the provider rather than the name, which is a bit
less reliable.

If you are installing Salt via git/pip, the formula will try to overwrite your
install with packaged versions. This setting makes it possible to avoid that.

Using a variable named salt is a bad idea when salt already has a variable
named salt.

Update sls files to match name change in map.jinja.

Added map.jinja solution more in line with other formulas,
This also improves issue #30

and pull request #30