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>