Add an `--ignore` flag to `podman image rm` to instruct ignoring image
if a specified image does not exist and to not throw an error. Other
commands (e.g., `podman container rm`) already support this flag.
Such an `--ignore` flag can come in handy in clean-up scripcts such as
the teardown phases in the Podman tests.
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>
95dad4d8a4