Update stemcell for shelshock

[#79489562]
Bump src/cf-mysql-broker

Bump cloudfoundry/cf-mysql-broker:
  Ruthie Byers:
     Commit to test autobump in cf-release ( Travis Success: https://travis-ci.org/cloudfoundry/cf-mysql-broker/builds/36712325 )
Increase timeout for mariadb exectuable to 5 minutes