Fix bashisms in image.sh shell scripts

Replace '&>/dev/null' output redirections to '>/dev/null 2>&1'.
Merge pull request #421 from Ledest/master

Fix bashisms in image.sh shell scripts

image.sh are shell scripts with shebang '/bin/sh'. But '&>' output redirection is
the nonstandard bash-specific construction that may be unsuported in other
POSIX-compatible shells