fix(os): pass pkgrepo state on unsupported os

[noelmcloughlin]

This PR avoids salt.pkgrepo state and/or rendering errors on MacOS/FreeBSD/Arch.

For example on Archlinux....

Data failed to compile:
----------
    Specified SLS salt.pkgrepo.arch in saltenv base is not available on the salt master or through a configured fileserver

[noelmcloughlin]

Verified salt-formula on Archlinux.

----------
          ID: salt-pkgrepo-install-saltstack-norepo-arch
    Function: test.show_notification
      Result: True
     Comment: No official repository for Arch
     Started: 09:13:59.794797
    Duration: 0.247 ms

... etc ...

-------------
Succeeded: 12 (changed=5)
Failed:     0
-------------
Total states run:     12

[noelmcloughlin]

Verified salt-formula on MacOS.

----------
          ID: salt-pkgrepo-install-saltstack-norepo-macos
    Function: test.show_notification
      Result: True
     Comment: No official repository for MacOS
     Started: 09:13:59.794797
    Duration: 0.247 ms

... etc ...

[noelmcloughlin]

One Travis CI failure is unrelated

[saltstack-formulas-travis]

🎉 This PR is included in version 0.58.2 🎉

The release is available on GitHub release

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