Adjust the revocation list test.

On some CI systems, running the test with -test.race takes longer to
complete, and therefore it might not be exactly 1 second between
revocations. It should still, however, not be the complete revocation
list.
Flipped the logic on the last test change.
Add ContextList.

It is now possible to return a list of all non-administrative contexts
present in the vault.