Following commit adds buildkit like support for `from` field to `--mount=type=bind`
and `--mount=type=cache` so images and stage can be used as mount source.
Usage looks like
```dockerfile
RUN --mount=type=bind,source=.,from=<your-image>,target=/path ls /path
```
and
```dockerfile
RUN --mount=type=cache,from=<your-image>,target=/path ls /path
```
Signed-off-by: Aditya Rajan <arajan@redhat.com>
Aditya Rajan