Clifford simulator result() fails on any circuit

[mtreinish]

Informations

• Qiskit Terra version: Latest master
• Python version: 3.7
• Operating system: Linux

What is the current behavior?

When attempting to call execute() with the backend being the clifford simulator it always fails.

This was hit in trying to add some new tests that ran on all backends:

https://travis-ci.org/Qiskit/qiskit-terra/jobs/442859915#L1694

1: concurrent.futures.process._RemoteTraceback: 
1: """
1: Traceback (most recent call last):
1:   File "/opt/python/3.5.6/lib/python3.5/concurrent/futures/process.py", line 175, in _process_worker
1:     r = call_item.fn(*call_item.args, **call_item.kwargs)
1:   File "/home/travis/build/Qiskit/qiskit-terra/qiskit/backends/aer/qasm_simulator.py", line 151, in _run_job
1:     if 'config' in qobj:
1: TypeError: argument of type 'Qobj' is not iterable
1: """
1: 
1: The above exception was the direct cause of the following exception:
1: 
1: Traceback (most recent call last):
1:   File "/home/travis/build/Qiskit/qiskit-terra/test/python/test_result.py", line 136, in test_add_aer
1:     result_a = qiskit.execute(qc1, backend).result()
1:   File "/home/travis/build/Qiskit/qiskit-terra/qiskit/backends/aer/aerjob.py", line 37, in _wrapper
1:     return func(self, *args, **kwargs)
1:   File "/home/travis/build/Qiskit/qiskit-terra/qiskit/backends/aer/aerjob.py", line 92, in result
1:     return self._future.result(timeout=timeout)
1:   File "/opt/python/3.5.6/lib/python3.5/concurrent/futures/_base.py", line 405, in result
1:     return self.__get_result()
1:   File "/opt/python/3.5.6/lib/python3.5/concurrent/futures/_base.py", line 357, in __get_result
1:     raise self._exception
1: TypeError: argument of type 'Qobj' is not iterable

Steps to reproduce the problem

Build any circuit and run execute() and result() on it with the clifford simulator backend. For example:

import qiskit
                          
qr = qiskit.QuantumRegister(2)
cr = qiskit.ClassicalRegister(2)
qc = qiskit.QuantumCircuit(qr, cr)

qc.h(qr[0])
qc.measure(qr, cr)
    
qiskit.execute(qc, 'clifford_simulator').result()

What is the expected behavior?

The circuit runs on the simulator.

Suggested solutions

Fix the underlying issue