Added support for new pydot versions to fix find_graphviz error (#6398)

* Added support for the new pydot API to fix find_graphviz error

* Simplified pydot installation checking

* Workaround for pydot generic Exception raising

* Removed hacky workaround for pyplot Exception, included comment

keras/utils/vis_utils.py

@@ -13,7 +13,10 @@
 
 
 def _check_pydot():
-    if not (pydot and pydot.find_graphviz()):
+    try:
+        # Attempt to create an image of a blank graph to check the pydot/graphviz installation.
+        pydot.Dot.create(pydot.Dot())
+    except Exception:  # pydot raises a generic Exception here, so no specific class can be caught.
         raise ImportError('Failed to import pydot. You must install pydot'
                           ' and graphviz for `pydotprint` to work.')