Fix of an environment problem affecting 2stage processing

[sawenzel]

Under certain conditions, the environment for tasks running under an alternative (2nd-stage) software tag lacked variables from the global-init section. This affected for instance the CCDB caching and led to inconsistent MC workflows.

This is now fixed with this commit. Thanks to @shahor02 for finding the issue.

[github-actions]

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[sawenzel]

@ktf : The CI appears unusually slow. It's been 16hours that this PR is open and still testing has not started. Getting this PR in is a bit urgent as it fixes an important bug.

[ktf]

@singiamtel can you have a look at this one as well?