Title: #546: TESTS: Re-add tests for `kdestroy -A`
On my up-to-date F-27 this test already passes with krb5-libs-1.15.2-8.fc27.x86_64. I
started CI but I don't have the results yet.
The only small issue is how to make sure that on other platforms where the test might
fail, it is at least easy to see why it fails. So I would propose to either move the test
with 3 principals to a separate function and add a doc comment or at least add a better
comment that this might fail due to a krb5 bug.
See the full comment at https://github.com/SSSD/sssd/pull/546#issuecomment-384774349