We had to introduce a web page to bootstrap the web version of devtools
because since https://bugs.chromium.org/p/chromium/issues/detail?id=1232509
chrome debugger port no longer serve such a page via HTTP.

The URL also changed, /serve_file/@{version_hash}. pattern is no longer
used, both the devtools and the websocket endpoint are in /devtools

The test was made a bit more complete by actually making requests and
trying to connect to websocket endpoints.

Some problems were found with incognito and block-new-web-contents
options:
 - they are boolean type, but the software parameter serialisation is
 XML, which as of today does not support boolean types. This is left
 TODO for now
 - When both --incognito and --block-new-web-contents are true, the
 command line flag was --incognito--block-new-web-contents, which is
 unknown and was ignored. Some minmal changes are included to fix this.