Fix WorkerState type to string in GetOrphanedVolumes.
Fix WorkerState type to string in GetOrphanedVolumes.

[#140339899]

Signed-off-by: Maria Shaldibina <dc03896a0185453e5852a5e0f0fab6cbd2e026ff@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse