Cannot instantiate Aer credentials for some coupling_map_type

[nkanazawa1989]

Environment

• Prefect Qiskit version: 0.1.1
• Python version: any
• Operating system: any

What is happening?

I cannot spawn client of QiskitAerCredentials with coupling_map_type

• heavy-hex
• heavy_square
• hexagonal
• grid

These coupling map types don't take num_qubits in the factory method, while QiskitAerCredentials specifies only num_qubits.

How can we reproduce the issue?

Create QiskitAerCredentials with, for example, num_qubits=12 and coupling_map_type="heavy-hex" (this should be okey, but error raised due to API mismatch).

What should happen?

I can create a client (.get_client) for any type of coupling_map_type as long as qubit number conforms to the lattice topology.

Any suggestions?

Infer coupling map parameter from num_qubits. When qubit number doesn't match with the topology raise an error.