This fixes a regression based on expectations of the runtime:
```
docker pull arm32v7/alpine
docker run arm32v7/alpine
```
Without this change, the `docker run` will fail due to platform
matching on non-arm32v7 systems, even though the image could run
(assuming the system is setup correctly).
This also emits a warning to make sure that the user is aware that a
platform that does not match the default platform of the system is being
run, for the cases like:
```
docker pull --platform armhf busybox
docker run busybox
```
Not typically an issue if the requests are done together like that, but
if the image was already there and someone did `docker run` without an
explicit `--platform`, they may very well be expecting to run a native
version of the image instead of the armhf one.
This warning does add some extra noise in the case of platform specific
images being run, such as `arm32v7/alpine`, but this can be supressed by
explicitly setting the platform.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>