Failure in volume.FS List is ignored

[MikaelSmith]

If find in volume.FS's List fails, the error is logged but the ls call still succeeds (exits 0) and reports the directory as empty. It should fail and return the error.

[MikaelSmith]

A little more context on this: volume.FS swallown the error because we may get useful output even if find exits non-zero due to lack of permissions on some targets. However, we also ignore stderr. Some possible improvements here are

• warn instead of info for errors when we get some entries back
• error if we get non-zero exit and no entries
• capture stderr; on failure, stdout probably doesn't contain the cause

Specific test was ls on the filesystem for a Bolt target that doesn't exist.