improve log formatting

Hi, I got improvement for formatting logs send by zabbix plug in. Shellescape is a good solution to avoid "shell injection", but it makes logs unreadable e.g : 
\ \ \ \ \ \ \ \ \<saml:AttributeValue\ xsi:type\=\"xs:string\"\ xmlns:xs\=\"http://www.w3.org/2001/XMLSchema\"\ xmlns:xsi\=\"http://www.w3.org/2001/XMLSchema-instance\"\>\`cat\ /dev/urandom\ \>\ /dev/null\`\</saml:AttributeValue\>

Instead shellescape I propose to use popen introduced in Ruby 1.9, which bypass shell.