Summary:
Use pipe2 with O_CLOEXEC to not leak FDs and close the pipe completely after reading.

BUG: 378268

Test Plan:
Did not break anything here, but I don't have MD RAID.
According to the reporter this fixed the FD leak issue.

Reviewers: #plasma, mart

Reviewed By: #plasma, mart

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D13664