Set ZOOCFGDIR env var to /stackable/rwconfig via product config

[maltesander]

Description

This works around https://issues.apache.org/jira/browse/ZOOKEEPER-4985
If we don't set this variable most of the shell scripts will fail (definitely zkCleanup.sh).
It can be set manually before every call but we do know the location of the config directory so no harm in making it a bit easier.

• Add the ZOOCFGDIR via product config to /stackable/rwconfig

Definition of Done Checklist

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Author

• Changes are OpenShift compatible
• CRD changes approved
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Reviewer

• Code contains useful comments
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Acceptance

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[lfrancke]

LGTM