Upgrade migration scripts discard stdout and stderr

[Joseph Richard]

Brief Description
-----------------
Upgrade migration script run with both stdout and stderr directed to /dev/null, which could cause important information to be lost.
See https://opendev.org/starlingx/config/src/branch/master/controllerconfig/controllerconfig/controllerconfig/upgrades/utils.py#L80

Severity
--------
Minor. Could make diagnosing failures harder.

Steps to Reproduce
------------------
Run upgrade migration script that outputs to stdout or stderr

Expected Behavior
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Output is captured

Actual Behavior
----------------
Output is discarded

Reproducibility
---------------
100%

Test Activity
-------------
Developer Testing

[Ghada Khalil (gkhalil)]

Low priority - would be nice to fix, but shouldn't hold up any release

[Ghada Khalil (gkhalil)]

Assigning to John Kung to decide whether this should be something to address in the future as a low priority improvement.