On my system, /proc/mounts sometimes contains a line like
```
udev /media/zhuowei/redhd/pmbootstrap/chroot_native/dev/loop0p2\040(deleted)
devtmpfs rw,relatime,size=1959476k,nr_inodes=489869,mode=755 0 0
```
The "\040(deleted)" text confuses `pmbootstrap shutdown`. Remove the suffix
if we find it in a /proc/mounts entry. This fixes#545.