test/certs/generate.sh: should regenerate when new service names are added

[jsha]

After a recent pull, I was getting errors running the integration tests because test/certs/ipki/sfe.boulder/ didn't exist. That's because sfe.boulder was recently added to the list of services, but generate.sh doesn't regenerate the certificates if the ipki directory already exists:

boulder/test/certs/generate.sh

Lines 70 to 74 in 161ca1e

	if ! [ -d ipki ]; then
	echo "Generating ipki/..."
	ipki
	fi

This error will affect anyone running Boulder, any time we add services to the internal PKI. We should improve the script so it automatically adds new services; for instance we could make the script check the existence of each service name's directory, rather than ipki overall.