OpenStack subnet info issue

I've installed Devstack with 2 nodes - first all-in-one installation, second compute node installation.
Openstack version:
```
$ nova-manage version
14.0.0
```
I have the following networks:
```
$ neutron net-list
+--------------------------------------+---------+----------------------------------------------------------+
| id | name | subnets |
+--------------------------------------+---------+----------------------------------------------------------+
| da04d56f-d51d-4d55-b816-a9d3f6e8f54f | private | 6809dbb9-0bb8-46bc-9bf0-b4bd9c7ac897 10.0.0.0/24 |
| | | 90f8868b-c967-497e-bbb1-f4dd5ef847ca fd7b:720e:cae8::/64 |
| e01e1f87-f5fa-4734-9595-a97517072b28 | public | 2cc03feb-7428-4a1d-a5d4-c4443d4bda77 2001:db8::/64 |
| | | 44a151d9-c807-44ce-aada-731dda7c22b3 172.24.4.0/24 |
+--------------------------------------+---------+----------------------------------------------------------+
```
And the following subnets:
```
$ neutron subnet-list
+--------------------------------------+---------------------+---------------------+-------------------------------------------------------------------------------+
| id | name | cidr | allocation_pools |
+--------------------------------------+---------------------+---------------------+-------------------------------------------------------------------------------+
| 2cc03feb-7428-4a1d-a5d4-c4443d4bda77 | ipv6-public-subnet | 2001:db8::/64 | {"start": "2001:db8::1", "end": "2001:db8::1"} |
| | | | {"start": "2001:db8::3", "end": "2001:db8::ffff:ffff:ffff:ffff"} |
| 44a151d9-c807-44ce-aada-731dda7c22b3 | public-subnet | 172.24.4.0/24 | {"start": "172.24.4.2", "end": "172.24.4.254"} |
| 6809dbb9-0bb8-46bc-9bf0-b4bd9c7ac897 | private-subnet | 10.0.0.0/24 | {"start": "10.0.0.2", "end": "10.0.0.254"} |
| 90f8868b-c967-497e-bbb1-f4dd5ef847ca | ipv6-private-subnet | fd7b:720e:cae8::/64 | {"start": "fd7b:720e:cae8::2", "end": "fd7b:720e:cae8:0:ffff:ffff:ffff:ffff"} |
+--------------------------------------+---------------------+---------------------+-------------------------------------------------------------------------------+
```
And I trying to run:
```
./pkb.py --cloud=OpenStack --machine_type=m1.medium --openstack_network=private --benchmarks=ping --image=cirros-0.3.4-x86_64-uec
```

And I've faced with a problem:
```
2016-12-13 16:17:26,235 ec18c1e2 MainThread INFO Verbose logging to: /tmp/perfkitbenchmarker/runs/ec18c1e2/pkb.log
2016-12-13 16:17:26,236 ec18c1e2 MainThread INFO PerfKitBenchmarker version: v1.9.0-78-ge00c40b
2016-12-13 16:17:26,237 ec18c1e2 MainThread INFO Flag values:
--machine_type=m1.medium
--openstack_network=private
--image=cirros-0.3.4-x86_64-uec
--cloud=OpenStack
--benchmarks=ping
2016-12-13 16:17:26,644 ec18c1e2 MainThread WARNING The key "flags" was not in the default config, but was in user overrides. This may indicate a typo.
2016-12-13 16:17:26,847 ec18c1e2 MainThread ping(1/1) INFO Provisioning resources for benchmark ping
2016-12-13 16:17:26,851 ec18c1e2 Thread-2 ping(1/1) INFO Testing OpenStack CLI command is installed and working
2016-12-13 16:17:26,852 ec18c1e2 Thread-2 ping(1/1) INFO Running: openstack image list --format json
2016-12-13 16:17:28,012 ec18c1e2 Thread-2 ping(1/1) INFO Validating prerequisites.
2016-12-13 16:17:28,014 ec18c1e2 Thread-2 ping(1/1) INFO Running: openstack image show cirros-0.3.4-x86_64-uec --format json
2016-12-13 16:17:29,073 ec18c1e2 Thread-2 ping(1/1) INFO Running: openstack flavor show m1.medium --format json
2016-12-13 16:17:30,426 ec18c1e2 Thread-2 ping(1/1) INFO Running: openstack network show private --format json
2016-12-13 16:17:31,514 ec18c1e2 Thread-2 ping(1/1) INFO Prerequisites validated.
2016-12-13 16:17:31,514 ec18c1e2 Thread-2 ping(1/1) INFO Running: openstack security group show perfkit_sc_group --format json
2016-12-13 16:17:32,583 ec18c1e2 Thread-2 ping(1/1) INFO Running: openstack keypair create perfkit_key_ec18c1e2 --format json --public-key /tmp/perfkitbenchmarker/runs/ec18c1e2/perfkitbenchmarker_keyfi
le.pub
2016-12-13 16:17:33,578 ec18c1e2 Thread-2 ping(1/1) INFO Running: openstack network show private --format json
2016-12-13 16:17:33,583 ec18c1e2 Thread-3 ping(1/1) INFO Running: openstack network show private --format json
2016-12-13 16:17:34,763 ec18c1e2 Thread-3 ping(1/1) INFO Running: openstack subnet show 6809dbb9-0bb8-46bc-9bf0-b4bd9c7ac897, 90f8868b-c967-497e-bbb1-f4dd5ef847ca --format json
2016-12-13 16:17:34,816 ec18c1e2 Thread-2 ping(1/1) INFO Running: openstack subnet show 6809dbb9-0bb8-46bc-9bf0-b4bd9c7ac897, 90f8868b-c967-497e-bbb1-f4dd5ef847ca --format json
2016-12-13 16:17:35,891 ec18c1e2 Thread-3 ping(1/1) INFO Ran openstack subnet show 6809dbb9-0bb8-46bc-9bf0-b4bd9c7ac897, 90f8868b-c967-497e-bbb1-f4dd5ef847ca --format json. Got return code (1).
STDOUT:
STDERR: ResourceNotFound: No Subnet found for 6809dbb9-0bb8-46bc-9bf0-b4bd9c7ac897, 90f8868b-c967-497e-bbb1-f4dd5ef847ca

2016-12-13 16:17:35,892 ec18c1e2 MainThread ping(1/1) ERROR Exception occurred while calling PrepareVm():
Traceback (most recent call last):
File "/home/user1/PerfKitBenchmarker/perfkitbenchmarker/background_tasks.py", line 235, in Run
self.return_value = self.target(*self.args, **self.kwargs)
File "/home/user1/PerfKitBenchmarker/perfkitbenchmarker/benchmark_spec.py", line 389, in PrepareVm
vm.Create()
File "/home/user1/PerfKitBenchmarker/perfkitbenchmarker/resource.py", line 160, in Create
self._CreateDependencies()
File "/home/user1/PerfKitBenchmarker/perfkitbenchmarker/providers/openstack/os_virtual_machine.py", line 97, in _CreateDependencies
source_range = self._GetInternalNetworkCIDR()
File "/home/user1/PerfKitBenchmarker/perfkitbenchmarker/providers/openstack/os_virtual_machine.py", line 365, in _GetInternalNetworkCIDR
subnet_dict = json.loads(stdout)
File "/usr/lib/python2.7/json/__init__.py", line 339, in loads
return _default_decoder.decode(s)
File "/usr/lib/python2.7/json/decoder.py", line 364, in decode
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
File "/usr/lib/python2.7/json/decoder.py", line 382, in raw_decode
raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded
```

I think the problem lies in the fact that the command `openstack subnet show 6809dbb9-0bb8-46bc-9bf0-b4bd9c7ac897, 90f8868b-c967-497e-bbb1-f4dd5ef847ca --format json` pass 2 subnets in one time.
Is it a problem in PerfKitBenchmarker or is it missconfiguration?