Use run_in_chroot to suppress the shell not found error

This commit fixes the following error that caused by additionally installed shells such as ZSH on the host environment.
`chroot: failed to run command `/bin/zsh': No such file or directory`
Merge pull request #93 from yudai/fix_chroot_in_image_install_grub

Use run_in_chroot to suppress the shell not found error