Fix new-backup-{zfs,rsnapshot}'s attempt to find the target zpool with most available space

ROOT/DEBIAN/control

@@ -3,7 +3,7 @@ Priority: optional
 Section: otherosfs
 Maintainer: Frank Lee <rl201@cam.ac.uk>
 Architecture: all
-Version: 0.9-ch17
+Version: 0.9-ch18
 Depends: debian-zfs, postgresql, liblockfile-simple-perl, libdbi-perl, libjson-perl, libzfs-perl-chem, libnet-openssh-perl, libdbd-pg-perl, mbuffer
 Description: a backup system using ZFS
  Ported (well, mostly) from FreeBSD to a Sane OS.

ROOT/usr/lib/chem-zfs-backup-server/new-backup-rsnapshot

@@ -33,7 +33,7 @@ done
 if [ -z $TGT ] ; then
  echo No existing ZFS found
  # Find emptiest zpool
- ZPOOL=`zpool list -Ho name,free | grep -v zroot | sort -rnk2 | head -1 | awk ' { print $1 } '`
+ ZPOOL=`zfs list -H -oname -S avail -d0 | grep -v zroot | grep -v $SOURCE | head -n1`
  TGT=$ZPOOL/$FQDN
  echo Using $ZPOOL
 fi

ROOT/usr/lib/chem-zfs-backup-server/new-backup-zfs

@@ -29,7 +29,7 @@ done
 if [ -z $TGT ] ; then
  echo No existing ZFS found
  # Find emptiest zpool
- ZPOOL=`zpool list -Ho name,free | grep -v zroot | sort -rnk2 | head -1 | awk ' { print $1 } '`
+ ZPOOL=`zfs list -H -oname -S avail -d0 | grep -v zroot | grep -v $SOURCE | head -n1`
  TGT=$ZPOOL/$FQDN
  echo Using $ZPOOL
 fi