aux_pumas test failure in CAM

When attempting to run the `aux_pumas` test suite using cam tag `cam6_4_055`, there was a runtime failure for the following test:

`SMS_D_Ln9.ne30pg3_ne30pg3_mg17.F2000dev.derecho_intel.cam-outfrq9s_pumas_emulated`

with the error being:

```
Registering hist coord: bins_ncd(10) with length: 35
Begin loading neural nets
ERROR: ERROR: handle_errmsg: micro_pumas_cam_init: NetCDF: Malformed URL
```

Thus it looks like currently the PUMAS emulator, at least as configured in this test, isn't working correctly in CAM.

@Katetc @wkchuang