[TASK] Stabilize duplicate exception find script

This opens stdin for awk-grep for write only, otherwise the internal 
awk communication is messed up, thus ack is slightly less to dependend
on outer environment, e.g Bamboo.

Change-Id: I228643ee0698aa2c30aa52fc11024fc041d95d97
Resolves: #76758
Releases: master
Reviewed-on: https://review.typo3.org/48655


Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>