Default prepare script supports Postgres 12 and up

The default prepare script now uses appropriate options if it detects Postgres
12 or higher. The error handling still needs work though.

Update prepare script for newer Postgres

ROOT/DEBIAN/control

@@ -3,7 +3,7 @@ Priority: optional
 Section: otherosfs
 Maintainer: Chemistry COs <support@ch.cam.ac.uk>
 Architecture: all
-Version: 0.9-ch69
+Version: 0.9-ch70
 Depends: zfs-dkms, postgresql-9.5 | postgresql-9.4 , liblockfile-simple-perl, libdbi-perl, libjson-perl, libzfs-perl-chem, libnet-openssh-perl, libdbd-pg-perl, mbuffer, rsync, nfs-kernel-server, pv, libwww-curl-perl
 Description: a backup system using ZFS (repository 'backup-scheduler')
  Ported (well, mostly) from FreeBSD to a Sane OS.

ROOT/etc/chem-zfs-backup-server/zfs-rsync.d/prepare

@@ -42,6 +42,17 @@ if [ ! -f $CONFDIR/$SERVER/exclude ] ; then
  $SCP -q root@$SERVER:/var/adm/backup/package-files $CONFDIR/$SERVER/exclude
 fi
 
+if $SSH root@$SERVER id postgres >/dev/null 2>&1 ; then
+  PGVER=$($SSH root@$SERVER pg_lsclusters| awk -F '[. ]+' '/online/ { print $1 }')
+  if [[ -n "$PGVER" ]]; then
+    if (( "$PGVER" >= 12 )) ; then
+      $SSH root@$SERVER "umask 077; su -c 'pg_dumpall --clean' postgres |gzip -9 >/var/adm/backup/postgres" || echo Postgres failed on $SERVER
+    else
+      $SSH root@$SERVER "umask 077; su -c 'pg_dumpall --oids --clean' postgres |gzip -9 >/var/adm/backup/postgres" || echo Postgres failed on $SERVER
+    fi
+  fi
+fi
+
 $SSH root@$SERVER "
 # Ensure that things are not readable where they ought not to be
 umask 077
@@ -57,9 +68,6 @@ if [ -f /etc/mysql/my.cnf ] ; then
  [ -S \$SOCKET ] && which mysqldump >/dev/null 2>&1 && mysqldump  --defaults-file=/etc/mysql/debian.cnf --all-databases >/var/adm/backup/mysql
 fi
 
-# Dump PostgresSQL, if the postgres user has access
-id postgres >/dev/null 2>&1 && [ -d /var/run/postgresql/ ] && [ -x /usr/bin/pg_dumpall ] && ( su -c 'pg_dumpall --oids --clean' postgres |gzip -9 >/var/adm/backup/postgres || echo Postgres failed on $SERVER )
-
 # Dump LDAP, if we can
 which slapcat >/dev/null 2>&1 && slapcat >/var/adm/backup/ldap