Fix: use share dir to collect logs

[mtojek]

This PR modifies the "stack dump" logic to collect elastic-agent logs from a different directory.

Tested with: elastic-package stack dump -v

CI did the same thing and logs showed up under Artifacts tab.

[elasticmachine]

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• Start Time: 2021-12-16T11:17:51.464+0000

• Duration: 22 min 11 sec

• Commit: a8a149d

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Test	Results
Failed	0
Passed	451
Skipped	0
Total	451

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