also allow whitelisted admin clients to clean certs

During #728 a regression was introduced, denying the other whitelisted
admin clients cleaning/deletion of certificates:

2020-06-02T16:30:47.856+02:00 ERROR [qtp1105504743-114201] [p.t.a.rules] Forbidden request: puppetserver01.[...] access to /puppet-ca/v1/certificate_status/my.fancy.hostname (method :delete) (authenticated: true) denied by rule 'Allow nodes to delete their own certificates'.

The solution is to re-allow the entries within
@server_admin_api_whitelist, which usually contain "localhost" and the
fqdn of the puppetserver CA system.