Increase expiration timeouts on leases to avoid races in NoopBackend

[sgmiller]

NoopBackend is primed with a canned Response for many of the unit tests
in expiration_test.go. If on a slow machine a lease expires, the revocation
will trigger a request to the backend, which may race on the population
of the same Response instance being used by the unit test.

[ncabatoff]

Why such a modest increase? I didn't look very closely, but I didn't see any behaviour in these tests that rely on it being a short expiry. TestExpiration_RenewToken seems similar in spirit to TestExpiration_Renew and it uses an hour.

I would go up to at least 1s.

[sgmiller]

Sure, can do. I just assumed that if this was a rarely failing test, this would make it 2.5x less likely. But happy to increase further since that doesn't actually slow the test.