userguide: fix URL to create updates

/os/ URL contains all the package in the latest stable release
/updates/ URL contains only the update from the latest stable release

e.g. if we are on 6.5 all packages of 6.5 will be in /os/ while
all the updated released on top of that are in /updates/
commands: removing useless parameter from checkHostAttr
commands: remove useless paramters from checkApplianceAttr
commands: escape attribute values for < > &

This is necessary in order to avoid breaking the kickstart XML, if
any attribute contains & < or > it will cause the kickstart to break

With this patch all the set and add attr command do the XML escaping
commands: remove useless code