Useful to answer the question of what the hash was at the point of some older
commit.
$ make --no-print-directory -C pkg/init/ show-tag
linuxkit/init:36c56f0664d49c5a6adc1120d1bf5ba6ac30b389
$ make --no-print-directory -C pkg/init/ show-tag HASH_COMMIT=4699f80ef73141ee87a77d03f93065e541fab382
linuxkit/init:17693d233dd009b2a3a8d23673cb85969e1dce80
Signed-off-by: Ian Campbell <ian.campbell@docker.com>