cli/autotest-rpc-migrate-host: Fix host migration script

This script was broken - using wrong web_server parameter when calling
frontend.AFE; also added user that can be specified on the command line
and removed the code that deletes the host from original server -
it is easy to do using other means but there are use cases when one
might want to keep it.

Signed-off-by: Julius Gawlas <julius.gawlas@hp.com>