volumes copying data unexpectedly

Fixes #8398
Prior to the volumes re-factor, data was not being copied on
volumes-from or host-mounted volumes.
After the re-factor, data was being copied for volumes-from.
This reverts this unintentional change in behavior.
@cpuguy83 Can we check against the expected error output by doing `err == nil || !strings.Contains(out, "...")` and `runCommandWithOutput(cmd)` ?