Ignition should be able to enable systemd aliases

[arithx]

Issue Report

Bug

Expected Behavior

When you enable a systemd alias the service should correctly be enabled on the resulting system.

Actual Behavior

Ignition writes a systemd-preset which explicitly does not work with aliases.

Other Information

I ran into this when re-writing the kola nfs tests trying to enable the nfsd.service resulted in nothing happening on the nfs host. Changing the unit being enabled to nfs-server.service fixed the issue.

[coreosbot]

Moved to coreos/ignition#583.