use same ssh method as in paas-bootstrap
use same ssh method as in paas-bootstrap

as-per https://github.com/alphagov/paas-bootstrap/pull/492

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