Allow setting variables for fixtures in a more generic way

[ekouts]

The docs say:

-S, --setvar=[TEST.]VAR=VAL
Set variable VAR in all tests or optionally only in test TEST to VAL.
TEST can have the form [TEST.][FIXT.]*, in which case VAR will be set in fixture FIXT of TEST. Note that this syntax is recursive on fixtures, so that a variable can be set in a fixture arbitrarily deep. TEST prefix refers to the test class name, not the test name, but FIXT refers to the fixture name inside the referenced test.

As far as I can tell [TEST.][FIXT.]* is not correct. We can set a variable in all the non-fixture tests with -Svar=val but for fixtures we have to do it manually since FIXT is not the class name but the name inside a test. Also * doesn't work for me at all, not sure what a valid example would be.

I think we should extend -S and allow setting fixture variables more easily.

This is also slightly related to #2626 , since -S strict_check=1 is not really equivalent to --strict.

[vkarak]

There are two parts in this issue, I think:

1. The fact that -S does not try to set variables in fixtures.
2. The fact that the . operator cannot be applied recursively in fixtures despite that being documented.

I think that the first is a feature request whereas the second seems like a bug to me. Perhaps we should separate them?

[ekouts]

Sure, I will leave this as new feature and open a new with the tag bug and documentation.