Deprecate engine_conf and prefer engine instead

To avoid having one set of options coming from `engine_conf`
and another set of options coming from `kwargs` and another set
coming from `engine_conf` if it is a URI just start to shift
toward `engine_conf` being deprecated and `engine` being a string
type only (or a URI with additional query parameters) and having
any additional **kwargs that are provided just get merged into the
final engine options.

This adds a new helper function that handles all these various
options and adds in a keyword argument `engine` that will be shifted
to in a future version (in that future version we can also then
remove the `engine_conf` and just stick to a smaller set of option
mechanisms).

It also adjusts all examples to use this new and more easier to
understand format and adjusts tests, conductor interface to use
this new more easily understandable style of getting an engine.

Change-Id: Ic7617057338e0c63775cf38a24643cff6e454950

taskflow/examples/persistence_example.py

@@ -91,20 +91,15 @@ else:
     blowup = True
 
 with eu.get_backend(backend_uri) as backend:
-    # Now we can run.
-    engine_config = {
-        'backend': backend,
-        'engine_conf': 'serial',
-        'book': logbook.LogBook("my-test"),
-    }
-
     # Make a flow that will blowup if the file doesn't exist previously, if it
     # did exist, assume we won't blowup (and therefore this shows the undo
     # and redo that a flow will go through).
+    book = logbook.LogBook("my-test")
     flow = make_flow(blowup=blowup)
     eu.print_wrapped("Running")
     try:
-        eng = engines.load(flow, **engine_config)
+        eng = engines.load(flow, engine='serial',
+                           backend=backend, book=book)
         eng.run()
         if not blowup:
             eu.rm_path(persist_path)
@@ -115,4 +110,4 @@ with eu.get_backend(backend_uri) as backend:
         traceback.print_exc(file=sys.stdout)
 
     eu.print_wrapped("Book contents")
-    print(p_utils.pformat(engine_config['book']))
+    print(p_utils.pformat(book))