Resolve "API does not provide facilities to communicate job and adhoc hostnames"

This MR extends the current API by introducing two new structures ADM_job_resources_t and ADM_adhoc_resources_t.

• ADM_adhoc_resources_t is renamed from ADM_storage_resources_t and now contains a list of nodes assigned for the adhoc storage instance (the PFS is more of a static thing, so it doesn't make sense to have a generic interface for this). An ADM_adhoc_resources_t argument is added to ADM_adhoc_context_create() and is propagated through RPCs. This allows resource managers (i.e. Slurm or the IC) to inform us about the nodes assigned for an adhoc_storage.
• A new structure ADM_job_resources_t is added to the API, which for now contains a list of nodes assigned to a job. An ADM_job_resources_t argumet is added to ADM_register_job() and related functions and is propagated to scord via RPCs. This allows resource managers to inform scord about the nodes assigned for a job.

Closes #59 (closed)