"defer cancelFunc()" causes the context to be cancelled already when
the t.Cleanup's are called, which causes strange test results if those
t.Cleanup's try to use that cancelled context to perform operations.
and also audit logs both the NotBefore and NotAfter of the issued cert.
Implemented by changing the return type of the cert issuer helpers
to make them also return the NotBefore and NotAfter values of the new
cert, along with the key PEM and cert PEM.
