Medium: Core: Post libxml conversion cleanup and fixes

• crm_element_value() - Don't use xmlGetProp(), it alloc's memory
• Only try to decompress fields with the BZ2 header - ignore fields like srcuuid
• create_xml_node() and crm_xml_add() don't need to alloc memory, xmlSetProp() and xmlNewChild() will do that for us
• Remove duplicate code

Mercurial revision: a5ae92f9e5e5d609b13a0448802dd912319442c2