SAML2: Allow SP name to be hostname
    
    This patch relaxes the allowed character set for SAML2 Service
    Provider names slightly to also allow the dash and period symbols.
    This allows the SP name to be an RFC-952 and RFC-1123 compatible
    hostname.
    
    https://fedorahosted.org/ipsilon/ticket/196
    
    Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>
    Reviewed-by: Pierre-Yves Chibon <pingou@pingoured.fr>