As discussed in  !248 this approach allows to set any mail header.

I also included a not so related patch of email header handlings 88d40b40 so that we review all this together.

/cc @gabriel @kazuhiko 

/reviewed-on !256

I just simulated an upgrade for an ERP5 running a version from before !185,  `ERP5UserManager Non Existence_constraint` properly disabled old `acl_users/erp5_users` and migrated all persons, but  `ERP5UserLoginManager Existence_constraint` did not activate `acl_users/erp5_login_users`.

This is because  `ERP5UserLoginManager Existence_constraint` is registered as a **pre-upgrade** constraint, but with my upgrade scenario, pre-upgrade constraint are installed too late. 

The upgrade scenario was:

 1. install new ERP5 SR on slapos
 2. manually install new versions of  erp5_upgrader and customer_configuration_upgrader business template
 3. run upgrade ( sense then fix on portal_alarms/promise_check_upgrade )

During step 3, when pre-upgrade constraints are executed, erp5_base is not installed yet, so  `ERP5UserLoginManager Existence_constraint` can not run because it's not installed yet. 

My suggestion is to change it to a post-upgrade constraint.

If I understand correctly and my upgrade scenario is really the supported one, it means we can only have pre-upgrade constraints in erp5_upgrader.

( I also fix a meaningless typo in the same code)

/cc @kazuhiko  @vpelletier @seb @gabriel 

/reviewed-on nexedi/erp5!262

To be able to use pre_upgrade we would need to install the bt first

Because of ERP5Type.UnrestrictedMethod, 'System Processes' can own objects.
Such objects can be proxy-role'd scripts, and proxy-role mechanism
triggers many users look-ups (each time security is evaluated, which is
virtually every getattr). Each such lookup will do a query for 'System
Processes' user, which will (hopefully) find nothing anyway.
So special-case 'System Processes' when looking by user_id by skipping
the search altogether (enforcing the inability to locate this user,
consistently with Zope assumptions, and consistently with previous
behaviour).

The code was not working as expected when we had several test nodes with same name
(which should not happen). So add a timestamp in the title.

test_result: fixed random issues where test result was staying confirmed while all tests were finished

When two test results line were stopped in parallel, both transactions were thinking that
there was still one ongoing test line, thus none of them were setting the test result in stopped.

Use activities instead of serialization to avoid having testnode getting conflict errors.

This makes a difference for SQLDict as not all messages are accepted for
insertion.

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

Charting libraries are better within iframe to avoid enabling too permissive
Content Security Policy globally

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

Add PortalType field to distinguish different types of Python Scripts, add referencence and use source code editor

We could not find a portable way to use verifyElementPositionRangeTop.

See internal discussion `[test][erp5] update selenium test` for more
details.

In addition to TypeEror when a 'date' is given, this also accepts duration=0.

If Test Result is associated with Test Node and thus distributor, and
distributor defines process timeout use this timeout to now when to
restart test lines. This is useful to avoid needless restart of tests
running on nodes related to long time outing distributors.

Otherwise fallback to default.

This link allows to navigate from Test Result via its Test Result Node
to Test Node and distributor related to given Test Result.

Note: It happens only, if client will do subscribeNode before calling
createTestResult.

This is accompanying commit to "erp5_test_result: stop affecting last
remaining tests to all test nodes", where alarms redrafts running tests
for long running nodes.

In case of very long running test nodes, to which support is introduced
in this work, it is acceptable situation that test will get redrafted
and shall be stopped.

Unfinished test
(test_18_checkConfigurationGenerationERP5ScalabilityDistributor) uses
return value of subscribeNode and assumes it is ERP5 object.

This work changes return value of subscribeNode to JSON object,
following startTestSuite return value, thus rendering this test failure.

As test is unfinished, non asserting part has been commented out.

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.

Extend subscribeNode to send configuration provided by user.

ERP5ProjectUnitTestDistributor allows to define maximum process timeout
of testnodes attached to it.