Add `responsetime_threshold` to Pingdom checks
Add `responsetime_threshold` to Pingdom checks

We had not set `responsetime_threshold` which means that the default of
30000 ms is used.

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