op-mode: T5633, T6465: fix error when op cmd interrupted, updates some system call syntax (backport #3731)

[mergify]

Change Summary

Replaces previous PR which I closed by accident: #3700

Summary:
Add exception catching for broken pipe error to exit gracefully when user stops program output. Resolves T5633: Bug 1 and 3

Corrects syntax for invoked "show ipv6 route bgp" command

Updates syntax for invoked show system image version / show system image storage to new CLI syntax

Note: Bug 2 identified in T5633 is non-breaking but has not been solved in this PR. I've narrowed the issue down to the underlying vyatta-op-cmd-wrapper shell code. I'm proposing to open a new Maniphest ticket specifically on this bug and close T5633 when PR is merged that way it's separated from this work and still visible as a bug to be fixed in the future.

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/T5633 bugs 1 and 3
https://vyos.dev/T6465

Related PR(s)

Component(s) name

Proposed changes

See above for changes.

How to test

Smoketest result

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

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This is an automatic backport of pull request #3731 done by [Mergify](https://mergify.com).

[github-actions]

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PR title 'op-mode: T5633, T6465: fix error when op cmd interrupted, updates some system call syntax (backport #3731)' does not match the required format!. Valid title example: T99999: make IPsec secure