Use all SSSD domains for info plugin by default.
    
    Rather than requiring --info-sssd-domain as an argument make it
    an optional argument, defaulting to enabling all SSSD domains.
    
    Convert the argument from a single value into a list so that multiple
    invocations can be made and all domains in the list will be enabled.
    
    There is still the possibility that failures in configuring a domain
    will occur (no domain found, for example) and these are considered
    "soft" failures. That is it won't abort the server installation.
    
    https://fedorahosted.org/ipsilon/ticket/78
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>