[rllib] Clean up agent resource configurations (#3296)

Closes #3284

python/ray/tune/ray_trial_executor.py

@@ -29,6 +29,8 @@ class RayTrialExecutor(TrialExecutor):
         self._avail_resources = Resources(cpu=0, gpu=0)
         self._committed_resources = Resources(cpu=0, gpu=0)
         self._resources_initialized = False
+        if ray.is_initialized():
+            self._update_avail_resources()
 
     def _setup_runner(self, trial):
         cls = ray.remote(
@@ -257,7 +259,16 @@ class RayTrialExecutor(TrialExecutor):
                 self._committed_resources.cpu, self._avail_resources.cpu,
                 self._committed_resources.gpu, self._avail_resources.gpu)
         else:
-            return ""
+            return "Resources requested: ?"
+
+    def resource_string(self):
+        """Returns a string describing the total resources available."""
+
+        if self._resources_initialized:
+            return "{} CPUs, {} GPUs".format(self._avail_resources.cpu,
+                                             self._avail_resources.gpu)
+        else:
+            return "? CPUs, ? GPUs"
 
     def on_step_begin(self):
         """Before step() called, update the available resources."""