Fix ipa-replica-install when key not protected by PIN
    
    When ipa-replica-install is called in a CA-less environment, the certs,
    keys and pins need to be provided with --{http|dirsrv|pkinit}-cert-file and
    --{http|dirsrv|pkinit}-pin. If the pin is not provided in the CLI options,
    and in interactive mode, the installer prompts for the PIN.
    The issue happens when the keys are not protected by any PIN, the installer
    does not accept an empty string and keeps on asking for a PIN.
    
    The fix makes sure that the installer accepts an empty PIN. A similar fix
    was done for ipa-server-install in
    https://pagure.io/freeipa/c/4ee426a68ec60370eee6f5aec917ecce444840c7
    
    Fixes:
    https://pagure.io/freeipa/issue/7274
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>