containers: T4473: Fix create container with not exist network

[sever-sever]

Change Summary

Fix for a setting container without or wrong network declaration

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://phabricator.vyos.net/T4473

Component(s) name

container

Proposed changes

How to test

Create a container with a nonexistent network
Current behavior:

set container name alp01 image alpine
set container name alp01 network NET02

Traceback (most recent call last):
  File "/usr/libexec/vyos/conf_mode/container.py", line 367, in <module>
    verify(c)
  File "/usr/libexec/vyos/conf_mode/container.py", line 135, in verify
    if network_name not in container['network']:
KeyError: 'network'

After Fix:

set container name alp01 image alpine
set container name alp01 network NET02

vyos@r14# commit
[ container ]
Container network "NET02" does not exist!

[[container]] failed
Commit failed
[edit]
vyos@r14# 

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly