Fix up all 0 serial check.

[robputt]

Issue

• Link: Use proc/cpuinfo for hardware serial #496
• Summary:

How

Screenshots

References

Checklist

• Tests added
• Cleaned up commit history (rebase!)
• Documentation added
• Thought about variable and method names

[sonarqubecloud]

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0.0% Duplication

[shawaj]

@robputt we should add test cases for:

Case 1:
/proc/cpuinfo All zero serial - 0000000000000000
/proc/device-tree/serial valid serial RockPi - d18dbe5c2a58cc61

Should return the second one

Case 2:
/proc/cpuinfo - All zero serial - 0000000000000000
/proc/device-tree/serial - All zero serial - 0000000000000000
Should return all 0s

Case 3:
/proc/cpuinfo - valid serial RasPi - 000000009e3cb787
/proc/device-tree/serial - valid serial RasPi - 000000009e3cb787
Should return the serial

Case 4:
/proc/cpuinfo - valid serial RockPi - d18dbe5c2a58cc61
/proc/device-tree/serial - valid serial RasPi - 000000009e3cb787
Should return the RockPi serial

I'm not sure there's any good way to test for an invalid serial? Unless those RockPi ones have a specific format @KevinWassermann94 or a fixed value?

[shawaj]

Also @robputt we should check for an empty serial there as well as all 0s, and revert to the other location as well in that case