Bug#858676: backports package cannot umount chroot cleanly on jessie

[Aron Xu]

Package: pbuilder
Version: 0.228.6~bpo8+1

Recent backport update of pbuilder/0.228.6~bpo8+1 cannot umount chroot
cleanly on jessie:

dpkg-buildpackage: info: full upload (original source is included)
I: copying local configuration
I: Copying back the cached apt archive contents
I: unmounting dev/pts filesystem
I: unmounting dev/shm filesystem
I: unmounting proc filesystem
I: unmounting sys filesystem
E: Something is still mounted under /tmp/pbuilder/10524; unmount and
remove /tmp/pbuilder/10524 manually
I: Current time: Fri Mar 24 21:32:45 CST 2017
I: pbuilder-time-stamp: 1490362365

Regards,
Aron