[fuel-devops] Environment creation fails with traceback if incorrect network settings for libvirt passed.

I've tried to create environment with my custom template, and creation failed with the following traceback: http://pastebin.com/dHVyY9qj

Steps to reproduce:
0) I used fuel-devops from master branch, latest commit - 104328e
1) Get the following template as example - http://pastebin.com/FLfBMyQX
2) Try to create environment using following command:

ENV_NAME="test" IMAGE_PATH=/path/to/image dos.py create-env template.yaml

Where /path/to/image is the path to image used for system storage, template.yaml is file that contains template described above by pastebin link.

Actual result:
As I said, creation failed with traceback. Devops created an entry in his database with provided name, it's possible to see environment in 'list' command as shown below:

$ dos.py list
NAME
------
test

$ dos.py net-list
NETWORK NAME IP NET
-------------- -------------
public 10.100.0.0/24
private 10.100.1.0/24

But there are no VMs created and only one network defined via libvirt:

$ virsh list --all
 Id Name State
----------------------------------------------------

$ virsh net-list --all
 Name State Autostart Persistent
----------------------------------------------------------
 default active yes yes
 test_public inactive yes yes

Expected result:
Human-readable error that network definition is incorrect, rollback database entries for environment just tried to create.