`device.gates_in_isa` does not handle all possible qubit types

[dahlend]

Pre-Report Checklist

• [x] I am running the latest versions of pyQuil and the Forest SDK
• [x] I checked to make sure that this bug has not already been reported

Issue Description

pyquil.device.gates_in_isa is not correctly reading the ISA of Aspen-9. From a quick read of: https://github.com/rigetti/pyquil/blob/55670be8c30f5365433bae55de001c630319a999/pyquil/device/_isa.py#L233 It looks like this does not handle the qubit.type==None, which is what is currently returned by Aspen-9

How to Reproduce

Code Snippet

import pyquil as pq
qc = pq.get_qc('Aspen-9')
isa = qc.device.get_isa()
pq.device.gates_in_isa(isa)

Error Output

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-4-ade0fcc7c65b> in <module>
      5 qc = pq.get_qc('Aspen-9')
      6 isa = qc.device.get_isa()
----> 7 pq.device.gates_in_isa(isa)

c:\<snip>\lib\site-packages\pyquil\device\_isa.py in gates_in_isa(isa)
    257             gates.extend([Gate("_", "_", [unpack_qubit(q.id)])])
    258         else:  # pragma no coverage
--> 259             raise ValueError("Unknown qubit type: {}".format(q.type))
    260 
    261     for e in isa.edges:

ValueError: Unknown qubit type: None

Environment Context

Operating System: Windows

Python Version (python -V): 3.7.4