ipa-client-install: autodiscovery must refuse single-label domains
    
    Since commit 905ab93, ipa-server-install refuses single-label domains,
    but older IPA server versions could be installed with a single-label
    domain/realm.
    ipa-client-install is already refusing single-label domain/realm when
    provided to the CLI with --domain / --realm but does not perform the same
    check when the domain is discovered.
    This commit adds a check to domain names automatically discovered and skips
    single-label domains. Same check for realm names.
    
    Fixes: https://pagure.io/freeipa/issue/7598
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>