Fix handling attributes with multiple values (e.g. groups)
    
    When handling attributes with more than one value provide a single
    saml:Attribute with multiple saml:AttributeValue's.
    
    I.e.
    
    
               NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic">
           <saml:AttributeValue>group1</saml:AttributeValue>
           <saml:AttributeValue>group2</saml:AttributeValue>
    </saml:Attribute>
    
    Not:
    
    
               NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic">
           <saml:AttributeValue>group1</saml:AttributeValue>
    </saml:Attribute>
    
               NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic">
           <saml:AttributeValue>group2</saml:AttributeValue>
    </saml:Attribute>
    
    This fixes handling of attributes with more than one value for pac4j
    based clients (Such as the Jenkins SAML plugin).
    
    Merges: #86
    Signed-off-by: Tom Judge <tomjudge@cisco.com>
    Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>