Add support for --interactive in mktree.podman

Pass this option, if specified, to $PODMAN.  This is needed for
unattended use of mktree.podman where no tty is allocated, such as
GitHub Actions.

Use it as follows:

  ./mktree.podman check --interactive=false ...

Default to true (by keeping -i in the command line) still, it allows
CTRL-C to work when running the script interactively.

Based on a patch by @Conan-Kudo.

tests/mktree.podman

@@ -35,9 +35,15 @@ case $CMD in
  exit 0
  ;;
  check)
+ # Pass select options to $PODMAN
+ case "$1" in
+ # Useful for CI environments without a tty
+ --interactive=*) OPTS=$1; shift ;;
+ *) OPTS= ;;
+ esac
  $PODMAN run --privileged -it --rm --read-only --tmpfs /tmp \
  -v /srv --workdir /srv -e ROOTLESS=$ROOTLESS \
- $IMAGE mktree check "$@"
+ $OPTS $IMAGE mktree check "$@"
  ;;
  reset)
  $PODMAN stop $NAME >/dev/null &&