Add back LocalCluster.__repr__.

LocalCluster.__repr__ was removed in dask#2675.

distributed/deploy/local.py

@@ -197,6 +197,13 @@ def __init__(
         )
         self.scale(n_workers)
 
+    def __repr__(self):
+        return "LocalCluster(%r, workers=%d, ncores=%d)" % (
+            self.scheduler_address,
+            len(self.workers),
+            sum(w.ncores for w in self.workers.values()),
+        )
+
 
 def nprocesses_nthreads(n):
     """