tests: don't use mount.<type> helpers in mount-by-pattern tests

tests: don't use mount.<type> helpers in mount-by-pattern tests

The test behavior is fragile if depends on external helpers. Let's
keep it based on mount(2) only. The test will be faster too.

Note that "mount -t <pattern>" does not behaviour as expected with
helpers. We need to try another helper if the current one ends with
status=1 (waitpid()). Now it returns status from the first helper.

Reported-by: Ruediger Meier <sweet_f_a@gmx.de>
Signed-off-by: Karel Zak <kzak@redhat.com>