tests: Generate a fresh OCSP response for each test run

tests: Generate a fresh OCSP response for each test run

GnuTLS has a hardcoded three day limit on OCSP response age regardless
of the next update value in the response. To make this work in the test
scripts, try to generate a new response when starting the authentication
server. The old mechanism of a response without next update value is
used as a backup option if openssl is not available or fails to generate
the response for some reason.

Signed-off-by: Jouni Malinen <j@w1.fi>