Adding intialize and finalize methods to workloads that will only be invoked once per run

- added initialze and finalize methods to workloads, which were the only
  major extension types that did not have them
- Semanatics for initialize/finalize for *all* Extensions are changed so
  that now they will always run at most once per run. They will not be
  executed twice even if invoke via istances of different subclasses (if
  those subclasses defined their own verions, then their versions will
  be invoked once each, but the base version will only get invoked
  once).

wlauto/core/instrumentation.py

@@ -288,9 +288,15 @@ def install(instrument):
             attr = getattr(instrument, attr_name)
             if not callable(attr):
                 raise ValueError('Attribute {} not callable in {}.'.format(attr_name, instrument))
-            arg_num = len(inspect.getargspec(attr).args)
-            if not arg_num == 2:
-                raise ValueError('{} must take exactly 2 arguments; {} given.'.format(attr_name, arg_num))
+            argspec = inspect.getargspec(attr)
+            arg_num = len(argspec.args)
+            # Instrument callbacks will be passed exactly two arguments: self
+            # (the instrument instance to which the callback is bound) and
+            # context. However, we also allow callbacks to capture the context
+            # in variable arguments (declared as "*args" in the definition).
+            if arg_num > 2 or (arg_num < 2 and argspec.varargs is None):
+                message = '{} must take exactly positional arguments; {} given.'
+                raise ValueError(message.format(attr_name, arg_num))
 
             logger.debug('\tConnecting %s to %s', attr.__name__, SIGNAL_MAP[stripped_attr_name])
             mc = ManagedCallback(instrument, attr)
@@ -379,6 +385,12 @@ class Instrument(Extension):
         self.is_enabled = True
         self.is_broken = False
 
+    def initialize(self, context):  # pylint: disable=arguments-differ
+        pass
+
+    def finalize(self, context):  # pylint: disable=arguments-differ
+        pass
+
     def __str__(self):
         return self.name