Bug after #2171

[junpenglao]

@ferrine
running examples/arbitrary_stochastic.py returns error after #2171:

Traceback (most recent call last):

  File "<ipython-input-7-612e002ded9a>", line 2, in <module>
    trace = pm.sample(n_samples)

  File "/usr/local/lib/python3.5/dist-packages/pymc3/sampling.py", line 240, in sample
    progressbar=progressbar, **args)

  File "/usr/local/lib/python3.5/dist-packages/pymc3/sampling.py", line 597, in init_nuts
    obj_optimizer=pm.adagrad_window

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/inference.py", line 755, in fit
    return inference.fit(n, **kwargs)

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/inference.py", line 123, in fit
    step_func = self.objective.step_function(score=score, **kwargs)

  File "/usr/local/lib/python3.5/dist-packages/pymc3/memoize.py", line 16, in memoizer
    cache[key] = obj(*args, **kwargs)

  File "/usr/local/lib/python3.5/dist-packages/theano/configparser.py", line 117, in res
    return f(*args, **kwargs)

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/opvi.py", line 258, in step_function
    total_grad_norm_constraint=total_grad_norm_constraint)

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/opvi.py", line 154, in updates
    total_grad_norm_constraint=total_grad_norm_constraint

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/opvi.py", line 186, in add_obj_updates
    obj_target = self(obj_z, more_obj_params=more_obj_params)

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/opvi.py", line 315, in __call__
    self.op.apply(self.tf),

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/operators.py", line 24, in apply
    return self.logq_norm(z) - self.logp_norm(z)

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/opvi.py", line 958, in logq_norm
    return self.logq(z) / self.normalizing_constant

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/opvi.py", line 598, in normalizing_constant
    tt.max([v.scaling for v in self.model.basic_RVs]))

  File "/usr/local/lib/python3.5/dist-packages/pymc3/variational/opvi.py", line 598, in <listcomp>
    tt.max([v.scaling for v in self.model.basic_RVs]))

AttributeError: 'MultiObservedRV' object has no attribute 'scaling'

[junpenglao]

This is introduced by the removal of https://github.com/pymc-devs/pymc3/pull/2171/files#diff-1f25198dab6a35cd27fffe043b7e1b9dL191