bump switchboard
bump switchboard

Submodule src/github.com/cloudfoundry-incubator/switchboard d294917..c434d13:
  > Add QueryBackendHealth method.

Signed-off-by: Rob Dimsdale-Zucker <4df639ba78cac7f8d741d02ef508f2611d6911dd@pivotal.io>

cloudfoundry/cf-mysql-release,cloudfoundry/cf-mysql-release,cloudfoundry/cf-mysql-release,cloudfoundry/cf-mysql-release