httpserver: tests: the script is using the wrong command line

There is no longer /usr/mgmt/httpserver.so installed in the image,
it's /libhttpserver.so now.

This patch changes the script so that it does not alter the command
line by default.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>