Resolve "server_id should not be optional in adhoc_storage"

This MR makes the server_id member in adhoc_storage explicit. The rationale is that constructors (for the C++ API) or .*_create() functions (for the C API) will most of the time be called from internal code, since client code will rely mostly on ADM_register_.*() to obtain handlers.

In this scenario, there's no possibility for the server_id "to not having been assigned yet", which is why it was optional in the first place.

Also, this MR renames the user_id to name, and the server_id to id.

Closes #74 (closed) #75 (closed)

src/common/api/admire_types.h

@@ -414,13 +414,15 @@ ADM_dataset_list_destroy(ADM_dataset_list_t list);
  *
  * @param[in] name A name for the storage tier
  * @param[in] type The type for the storage tier being created.
+ * @param[in] id The assigned id for the storage tier being created.
  * @param[in] ctx Some specific context information for the storage tier or
  * NULL if none is required. For instance, an adhoc storage system may find it
  * useful to provide an ADM_adhoc_context_t describing the instance.
  * @return A valid ADM_STORAGE if successful, or NULL in case of failure.
  */
 ADM_storage_t
-ADM_storage_create(const char* name, ADM_storage_type_t type, void* ctx);
+ADM_storage_create(const char* name, ADM_storage_type_t type, uint64_t id,
+                   void* ctx);
 
 /**
  * Destroy a ADM_STORAGE created by ADM_storage_destroy().