Improve public key generation script
Improve public key generation script

There has been confusion about whether to commit unplanned changes to
the generated public keys.

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf