Issue title: chroot can't execute '/system/bin/sh'
 Issue body: Rooted phone - Busybox is installed in /system/xbin

Installed ubuntu - trusty - armhf - 3072MB - /storage/emulated/0/linux.img

everything installed fine - container started well and vnc as well with user android

Cannot sudo su - (SET PERM ROOT error) so I opened Terminal Emulator and:

`su`
`cd /data/data/ru.meefik.linuxdeploy/files/bin`
`./linuxdeploy shell`

and I get : `chroot can't execute '/system/bin/sh' - no such file or directory`
 Comments: 
 Comment 0: Solved by restarting phone... have no explanation though but problem is solved.
 Comment 1: intall android4.1.2
{'source': 'GithubIssues', 'repo_name_with_owner': 'meefik/linuxdeploy', 'issue_id': 173636628, 'repo_stars': 4658.0}