nfs: Don't always consider the root directory to be virtual

Contrary to what the comment in getFileHandle said, it is not uncommon to set rootdir=/srv/nfs in /etc/nfs.conf and then export / in /etc/exports. In that configuration, the NFS server appears to be exposing its entire filesystem, but is in fact only exposing the subdirectory /srv/nfs. Handle that situation and list the directory contents instead of assuming that / is a virtual directory with no real files or directories inside of it.