Volume mounting logic introduced in #43775 and #45623 checks
for subPath existence before attempting to create a directory,
should subPath not be present.
This breaks if subPath is a dangling symlink, os.Stat returns
"do not exist" status, yet `os.MkdirAll` can't create directory
as symlink is present at the given path.
This patch makes existence check to use os.Lstat which works for
normal files/directories as well as doesn't not attempt to follow
symlink, therefore it's "do not exist" status is more reliable when
making a decision whether to create directory or not.
subPath symlinks can be dangling in situations where kubelet is
running in a container itself with access to docker socket, such
as CoreOS's kubelet-wrapper script
020ec43b56