Abort transaction, we do not need changes made by test to persist.

Execute pending activities before removing persons, the pending
activities might be relying on the existence of persons.

This changes API on a script that some projects have customized, but
getActiveUserPreferecnce "should work" even with an old script not
returning preferences.

In that case, first call to getActiveUserPreference will create
preference but not return it, but next time getActiveUserPreference is
called, the preference will probably be indexed and will be returned.

This method creates a user preference if no preference exists.

We do not need to pre-create user preferences, especially that creating
them too early creates one preferences for each person created in person
module and does not allow Person_createUserPreference to create
preference based on person's assignments are they are not created yet.

We do not need to clear cache when deleting user logins anymore. This
problem was fixed differently.

Adjust tests that was relying on cache being cleared when persons ar
deleted:

testERP5Web.TestERP5Web.test_15_Check_LastModified_Header was never
isolated from test_14.

test_14 was filling Base_getWebDocumentDrivenModificationDate cache and
this cache got clear when the persons where being deleted during
tearDown. When removing this interaction clearing cache, we revealed
this weakness. Choosen solution was to clear cache before checking
response headers, to make sure we don't get something filled by a
previous test.

Tests should not need to reindex modules

In the same time, stop showing range of cores like "9 to 15" cores. The infrastructure should be
important enough to have all the time the maximum of cores in the range. So just use the maximum
in the range, "15 cores" here.

Make sure we find section if we render https://my_site/my_section/foo.html. This is required
to take into account configuration of the web section, like specific content security policy.

Should make test output more expressive on failure.

To make it more likely detect killed transactions before entering
tpc_finish phase.

Saves one round-trip to server.

This parameter does not force a reconnection, it allows reconnecting if
a closed-connection is detected when querying on a transactional
connection on which the transaction was already started.

Otherwise, all subsequent tests fail too.

This reverts commit 699759bc

variation_category is implemented