Cron install / remove via command messes up stderr 2>&1 entries

[adrian-martinez-interactiv4]

Installing or removing crontab via command adds 2>&1 repeatedly, even for crontab entries not related with Magento, if they match a regular expression. See details below.

Preconditions

1. Magento2 develop branch
2. PHP 7.0.15

Steps to reproduce

1. Set up a crontab entry like this one:
   
2. Run bin/magento cron:install
3. Check crontab via crontab -l
4. Run bin/magento cron:remove
5. Check crontab via crontab -l

Expected result

1. Magento crontab gets installed, then removed and external crontab entry remains as it is

Actual result

1. After installed, additional 2>&1 gets added:
   
2. After removed, also additional 2>&1 gets added:
   

This also applies to other Magento2 installations crontab entries:

[magento-engcom-team]

@adrian-martinez-interactiv4, thank you for your report.
We've created internal ticket(s) MAGETWO-82533 to track progress on the issue.