Adding LXD Pod with pre-composed resources errors out

[Newell Jensen]

When trying to add a LXD Pod from the maas cli I get the below traceback. This has to do with the face that I had a pre-composed VM in LXD.

==> /var/log/maas/rackd.log <==
   File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1386, in _inlineCallbacks
     result = g.send(result)
   File "/usr/lib/python3/dist-packages/provisioningserver/drivers/pod/lxd.py", line 326, in discover
     cpu_speed=discovered_pod.cpu_speed,
   File "/usr/lib/python3/dist-packages/provisioningserver/drivers/pod/lxd.py", line 182, in get_discovered_machine
     storage_pool=pool,
   File "<attrs generated init 86327313f484cbc7ef217a50d76b6637e4e4ccc6>", line 4, in __init__
     self.size = __attr_converter_size(size)
 builtins.ValueError: invalid literal for int() with base 10: '20GB'