Firefox and Xvfb aren not provided by the tested SR,
but rather by a separate SR that is installed by the testnode.

Also if process_timeout is available in received configuration setup
process_manager with transmitted value.

Backward compatibility is assured, that if no process_timeout is
provided, nothing is being updated.

Also process_timeout not set on master (the default), will not change
local default.

Since a process might exit by himself at any time, handle exceptions when
we try kill processes

This prepares for the removal of --firefox_bin and --xvfb_bin options. The
API between the testnode and the tested software must be exclusively generic.

Conflicts:
	product/ERP5Type/tests/ERP5TypeFunctionalTestCase.py

/reviewed-on nexedi/erp5!505

/reviewed-on nexedi/erp5!346

This caused two problems:
 - If Xfvb was killed and left a stale lock file, we don't reuse this
   display. After some time we end up having "All display locked"
   exception but no Xvfb process running.
 - Xvfb's slapos is patched to store control sockets and lockfiles in
   $TMPDIR ( slapos@58462c24 ).
   We don't have $TMPDIR set in testnodes, but this would be a problem
   if we ever set it.

Because Xvfb can detect a stale lock file upon startup and start anyway,
the easy way running Xvfb for each display and see if it's still running
after a few seconds.

Conflicts:
	bt5/erp5_hal_json_style/SkinTemplateItem/portal_skins/erp5_hal_json_style/ERP5Document_getHateoas.py
	bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_pt_form_dialog_js.js
	bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_pt_form_dialog_js.xml

/reviewed-on nexedi/erp5!269

Fix error display after save
Fix parameters not recognized
Fix python linting
the same way as ERP5 Script Python