Bump src/switchboard/src/github.com/pivotal-cf-experimental/switchboard

Bump :
  Abhi Hiremagalur:
     Switch to our usual Apache 2.0 license
     Make healthcheck more idiomatic
  Raina Masand:
     Revising log messages
     Using single logger instance for switchboard
  Abhijit Hiremagalur and Raina Masand:
     Rename dummy_listener to dummy_backend
     Add integration test for failover
  Raina Masand and Stev Witzel:
     Have switchboard keep track of cluster health and serve or reject client connections accordingly
     Simplifying timeout logic in healtcheck
     Adding failover logic - Close client connection from main switchboard loop - Keep track of backend health, set active backend - Preliminary changes to main_test
     Remove SetActive and have SetHealthy/SetUnhealthy manage that work
     Added/tested SetHealthy, SetUnhealthy, Healthy
     Backends keeps track of backend state
     Filled in rest of backends tests for Active/SetActive/All
     Add simplified SetActive to backends
     Adding first set of unit tests for backends
  Abhi Hiremagalur and Stev Witzel:
     Move mutex unlock into go routine
     Remove semicolons
     Manage backends in synchronized struct
     Introduce 2nd backend in main_test
     no need reassign timeout again since it is assigned inside the for loop
     Rename local - backends to cluster
     Inline local
     Make internal attributes private
  Abhi Hiremagalur and Raina Masand:
     Backfill remaining backend unit tests
     Add unit test for backend.SeverConnections
     Avoid pollution
     Collapse backend.dial into backend.Bridge for conciseness
     Encapsulate creation of each bridge in bridges
     Introduce (incomplete) unit test for backend
     Encapsulate/hide Backend.dial implementation detail
     Remove unused field
     Backend does not need mutable methods
     make bridges safe to modify across goroutines
     DRY test setup
     Avoid exposing implementation details
     Remove redundant "Bridge" from method names
     Encapsulate (possibly) mutable slice
     Extract bridges collection
     Make switchboard immutable always
     Consitent capitalisation for Healthcheck
     Use lowercase for impl in interface/impl pair
     Make healthcheck immutable always
     Make bridge as immutable always
     Import switchboard into main.go without .
     Use counterfeiter for FakeBridge
     Use FakeReadWriteCloser instead of FakeConnection
     Move io fake into fakes package
     Move fakes to own files
     Rename local
  Abhi Hiremagalur and David Sabeti:
     Follow go convention for filename
     Move creation of Bridge into Backend
     Rename local var
     Backend is no longer a middleman for healthchecks
     Inject backend into healthcheck to avoid indirection
     Move routing into cluster
     Avoid defered connection closing
     Track currentBackendIndex on Backends
     Introduce Backend interface
     Extract Backends type
     Forgot to rename file
     Introduce interface for Backend
     Rename BackendManager to Switchboard
  David Sabeti and Rob Dimsdale:
     Healthcheck becomes property of Backend.
     Add bridge_test.go
  Raina Masand and Rob Dimsdale:
     Flags on switchboard accept lists of IPs/ports
  Ruthie Byers and Raina Masand:
     Extracted logic into BackendManager from main