This is especially important for distributions like NixOS where `/bin/bash` doesn't exist, or for MacOS users who've installed a newer version of Bash than the one that comes with their OS.
Signed-off-by: Andrew "Tianon" Page <admwiggin@gmail.com>
This drops support for migrations from pre-1.10 Docker versions, which
should be done via an external tool or an intermediate upgrade.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
