Allow customizing storage_capacity_mb

[#71061560]
Bump src/cf-mysql-broker

Bump cloudfoundry/cf-mysql-broker:
  Alex Stupakov and Rob Dimsdale:
     Support configurable capacity ( Travis Success: https://travis-ci.org/cloudfoundry/cf-mysql-broker/builds/28425044 )
Fixing test configuration

[#71061560]
Bump src/cf-mysql-broker

Bump cloudfoundry/cf-mysql-broker:
  Nicholas Calugar and Rob Dimsdale:
     Service instance manager raises error for non-existent plan ( Travis Success: https://travis-ci.org/cloudfoundry/cf-mysql-broker/builds/28445259 )