configtree: T5251: catch/raise errors in functions delete and delete_value

[jestabro]

Change Summary

The functions delete and delete_value should raise ConfigTreeError on a non-zero return value from the respective libvyosconfig functions.

This was a missing case in the implementation; all other functions raise error when appropriate.

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://vyos.dev/T5251

Component(s) name

Proposed changes

How to test

>>> from vyos.configtree import ConfigTree, ConfigTreeError
>>> with open('/config/config.boot') as f:
...     config_file = f.read()
... 
>>> config = ConfigTree(config_file)
>>> try:
...     config.delete(['interfaces', 'ethernet', 'eth999', 'address'])
... except ConfigTreeError as e:
...     print(e)
... 
Path doesn't exist: ['interfaces', 'ethernet', 'eth999', 'address']
>>> try:
...     config.delete_value(['interfaces', 'ethernet', 'eth0', 'address'], 'foo')
... except ConfigTreeError as e:
...     print(e)
... 
Value doesn't exist: 'foo'

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