Test listing should also list the fixture variable names since this is required by the `-S` option

[ekouts]

This is about the wrongly documented behavior of -S from #2757.

[vkarak]

It might also be a bug in the code and the documentation could just be correct. ;-) I'll have to look at it.

[vkarak]

So, the documentation is correct, but not so accurate. The FIXT refers to the fixture variable name, not the fixture class name. Add the following in the fetch_osu_benchmarks:

    @run_after('init')
    def foo(self):
        print(self.descr)

and then try this:

./bin/reframe -C tutorials/config/daint.py -c tutorials/fixtures/osu_benchmarks.py --skip-system-check --skip-prgenv-check -l -n osu_latency_test -S osu_latency_test.osu_binaries.osu_benchmarks.descr=hello -L

This will correctly print "hello." What is not clear from the docs is that FIXT refers to the class name and and there is no way to know the variable name from the test listing, which is confusing. I will expand the docs and update the test listing (perhaps in its detailed form, so as to print the fixture variable name).