lxd/storage/s3/miniod: Use a sub-directory for minio on storage volume
lxd/storage/s3/miniod: Use a sub-directory for minio on storage volume

 - Avoids any issues with directories created on the root volume by the filesystem intefering with MinIO.
 - Allows easier changing of ownership/permissions later if we want to run MinIO as unprivileged user.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

stgraber/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd