Mark getgroups()/setgroups() as non-blocking in BlockGuard tests.

Follow-up to commit 44177e6982a62506127a857070a2452956c3f0f1

Test: vogar BlockGuardOsTest
Change-Id: I7dacca4d1fe712f22bfd2f2e8722ca85e1f3f9f7
1 file changed