[tune] hyperband (#1156)

* trial scheduler interface

* remove

* wip median stopping

* remove

* median stopping rule

* update

* docs

* update

* Revrt

* update

* hyperband untested

* small changes before moving on

* added endpoints

* good changes

* init tests

* smore tests

* unfinished tests

* testing

* testing code

* morbugs

* fixes

* end

* tests and typo

* nit

* try this

* tests

* testing

* lint

* lint

* lint

* comments and docs

* almost screwed up

* lint

python/ray/tune/trial.py

@@ -142,12 +142,21 @@ class Trial(object):
         experiment. This results in a state similar to TERMINATED."""
 
         assert self.status == Trial.RUNNING, self.status
-        self.checkpoint()
-        self.stop()
-        self.status = Trial.PAUSED
+        try:
+            self.checkpoint()
+            self.stop()
+            self.status = Trial.PAUSED
+        except Exception:
+            print("Error pausing agent:", traceback.format_exc())
+            self.status = Trial.ERROR
+
+    def unpause(self):
+        """Sets PAUSED trial to pending to allow scheduler to start."""
+        assert self.status == Trial.PAUSED, self.status
+        self.status = Trial.PENDING
 
     def resume(self):
-        """Resume PAUSED tasks. This is a blocking call."""
+        """Resume PAUSED trials. This is a blocking call."""
 
         assert self.status == Trial.PAUSED, self.status
         self.start()