Make inspector listening port configurable

Currently we use fixed port 1337 as inspector port. When weblauncher is launched
by chromedriver it passes the inspector port as commandline argument
--remote-debugging-port=<port>. Later on chromedriver will try to communicate
with chrome via that port. We should use that port when starting devtools
HTTP handler.

Change-Id: I83e3341a535d50a129670bd0056b3ca448c8e2e5
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>