Increase paas-admin instance count to 6
Increase paas-admin instance count to 6

Recently, PagerDuty alerts were triggered by Pingdom for paas-admin. We
expect this to be due to locking up of instances during slow billing
queries.
This is meant as a  quick response to reduce the likelihood of being
called. It is not a fix.

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