tests: Extend test_child_common.c to include tests for the only_extra_args functionality Reviewed-by: Sumit Bose <sbose@redhat.com> Reviewed-by: Pavel Březina <pbrezina@redhat.com>

TESTS: Cover child_common.c with unit tests The module wasn't tested properly, which made it harder to patch it Reviewed-by: Pavel Březina <pbrezina@redhat.com>

tests: Free popt_context Nikolai Kondrashov <Nikolai.Kondrashov@redhat.com>

Rename test-child to dummy-child Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>