9187: Refactor dispatcher support into common library and update to use Locking API.

9187: Refactor dispatcher support into common library and update to use Locking API.

New dispatcher package in Go SDK provides framework for monitoring list of
queued/locked/running containers.  Try to lock containers in the queue; locked
or running containers are passed to RunContainer goroutine supplied by the
specific dispatcher.  Refactor existing dispatchers (-local and -slurm) to use
this framework.  Dispatchers have crash recovery behavior, can put containers
which are unaccounted in cancelled state.