Add logging to sinatra app for ci acceptance tests

Help fix flakiness seen on Dijon
Remove unused storage_capacity_mb from integration config

Removed from the script which generates it

[#74071960]
Bump src/cf-mysql-broker

Bump cloudfoundry/cf-mysql-broker:
  Alex Stupakov and Leo Rossignac-Milon:
     Renamed method in overhead computation for clarity ( Travis Success: https://travis-ci.org/cloudfoundry/cf-mysql-broker/builds/30128233 )