Extend Service Output for NFS Mounts (AIX + Linux)

@CFriedrich if you manually set the environment var MK_OSSTR for now, how does the following work out for you:

# Function to list NFS mounts for use by section_nfs

get_nfs_mounts() {
    if [ -r /proc/mounts ]; then
        awk '$3 ~ "nfs" {printf "%s on %s\n",$1,$2}' /proc/mounts
    else
        case "${MK_OSSTR}" in
            (aix)   mount | awk '$4 ~ "nfs" {printf "%s:%s on %s\n",$1,$2,$3}' ;;
            (linux) mount | awk '$5 ~ "nfs" {printf "%s on %s\n",$1,$3}' ;;
        esac
    fi
}