devtool: handle not running in a terminal
devtool: handle not running in a terminal

devtool was not handling not running in a terminal properly (e.g. when
using input/output/error pipes). Fixes:
- don't ask for user confirmation if STDIN is not attached to a
  terminal (i.e. fail unless -y/--unattended was specified);
- don't use colors if STDOUT is not attached to a terminal;
- don't use colors in error messages if STDERR is not attached to a
  terminal;
- properly pass (or don't pass) the terminal endpoints to the docker
  container.

Signed-off-by: Dan Horobeanu <de06b8d568359df57e57b444456da06d2313ae63@amazon.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker