Although bake is for running multiple targets, --set required a single
target name for overriding a property. This change allows matching
multiple targets for overrides.
Signed-off-by: Tibor Vass <tibor@docker.com>
This works just like the `build` command where if you have `--build-arg
FOO`, it will read the variable from env and only set a value if the
variable is defined.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
