Reduce number of cells to 21
Reduce number of cells to 21

This brings us in line with ADR021 based upon present utilisation.
Future additions may be required and should be based upon the monitor
triggering and requests to increase capacity from tenants.

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