Add new table experiment_keys to hold RSA priv/pub key pair and an SSH
public key derived from the private key.

Initialized when experiment is first created, I have not done anything
to set the keys for existing experiments yet.

But for testing, you can do this:

	use lib "/usr/testbed/lib";
	use Experiment;

	my $experiment = Experiment->Lookup("testbed", "layers");
	$experiment->GenerateKeys();