If a Dockerfile is using a `VOLUME` directive and the directory exists
in the rootfs, like in this example:

	FROM docker.io/library/alpine:latest
	VOLUME [ "/run" ]

The alpine container image already contains a "/run" directory. This
will force the code in WithVolumes() to copy its  content to the new
volume created for the VOLUME directive. This copies the content as well
as the ownership.

However, as we perform the mounts from the host POV without being inside
a userns, the idmap option will just shift the IDs in ways that will
screw up the ownerships when copied. We should only use the idmap option
when running the container inside a userns, so the ownerships are fine
(the userns will do a shift and the idmap another, to make it all seem
as if there was no UID/GID shift in the first place).

This PR does just that, remove the idmap option from mounts so we copy
the files without any ID transformations. It's simpler and easier to
reason about if we just don't mount with the idmap option here: all
files are copied just fine without ID transformations and ID
transformation is applied via the idmap option at mount time when
running the pod.

Also, note that `VOLUME` directives that refer to directories that don't
exist on the rootfs work fine (`VOLUME [ "/rata" ]` for example), as
there is no copy done in that case so the permissions weren't changed.

Signed-off-by: Rodrigo Campos <[email protected]>
(cherry picked from commit 41953f7)
Signed-off-by: Rodrigo Campos <[email protected]>