/etc/groups is not needed when specifying numeric group ids. This
change allows containers without /etc/groups to specify numeric
supplemental groups.
Signed-off-by: Sami Wagiaalla <swagiaal@redhat.com>
Update the tests to use the test-friendly GetAdditionalGroups API,
rather than making random files for no good reason.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>