show: T4581: 'show system cpu' fix

[goodNETnick]

Change Summary

Fix for 'show system cpu'

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/T4581

Component(s) name

opmode

Proposed changes

link op-mode command to the new script ("cpu.py", previously used "show_cpu.py")

How to test

show system cpu

Output:

vyos@vyos:~$ show system cpu
CPU socket: 0
CPU Vendor:       GenuineIntel
Model:            Intel(R) Core(TM) i7-3520M CPU @ 2.90GHz
Cores:            1
Current MHz:      2893.417

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