Use path within named volume once available

[nuest]

As described here, named volumes cannot be combined with paths within the volume.

This is required in muncher to mount the correct path to 2nd level containers when using a named volume with docker-compose, see source code occurences of config.fs.volume. The problem only occurs when mounting a specific path within the volume (i.e. manifest generation, metadata brokering after save in muncher), mounting the volume to the data directory (o2rplatform_o2rstorage:/tmp/o2r) to the 2nd-level container seems to work fine (metadata extraction and brokering in loader for example) when it is possible to provide the correct path to the tool in the 2nd-level container.

When moby/moby#32582 is closed, updated the respective FIXMEs.

[nuest]

TODO Try out if the same approach that works for metadata also works for manifest generation! Probably must extend containerit a bit for that.