Http Server: Modify the parameter order in path_holder

By modifying the parameter order in path holder, it is possible to add
the lambda expression directly as a parameter to the set_handler
function.

Now it is possible to write:
getOSversion.set_handler("json", [](const_req req)
    {
        return formatter::to_json(osv::version());
    });

the os.cc and jvm.cc where modified to use the shorten version

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>