Ensure pg-dump-script includes a dump of roles

We don't always need the role data, if the presumption is that we'll
be doing a pg_restore in conjunction with an ansible role which creates
all required roles. But, having a copy of the role data will never hurt!
It also gives us a straightforward way of restoring a database to a
standalone postgres instance without having to have provisioned a
dedicated VM with the relevant ansible roles.

ROOT/DEBIAN/control

@@ -3,6 +3,6 @@ Priority: optional
 Section: otherosfs
 Maintainer: Chemistry COs <support@ch.cam.ac.uk>
 Architecture: all
-Version: 0.9-ch83
+Version: 0.9-ch84
 Depends: zfs-dkms, postgresql-13 | 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')

ROOT/usr/lib/chem-zfs-backup-server/pg-dump-script

@@ -36,9 +36,11 @@ unset PGPASSFILE
 TEMPDIR=$(ssh ${SSHUSER}@${HOSTNAME} mktemp -d /tmp/pgXXXXX)
 
 MOUNT=$(zfs get -H -ovalue mountpoint $ZFSTARGET)
-BACKUP_DEST=$MOUNT/pgdumps/pgdumps-master/
+BACKUP_ROOT=$MOUNT/pgdumps
+PGDUMP_DEST=$BACKUP_ROOT/pgdumps-master/
+PGROLE_DEST=$BACKUP_ROOT/pg_roles
 
-mkdir -p $BACKUP_DEST
+mkdir -p $PGDUMP_DEST
 
 # we need this to exist for the rsync part of the backup, so the rsync returns successfully
 ssh ${SSHUSER}@${HOSTNAME} mkdir -p /var/empty
@@ -48,6 +50,11 @@ ssh ${SSHUSER}@${HOSTNAME} mkdir -p /var/empty
 # script which called us.
 ssh ${SSHUSER}@${HOSTNAME} pg_dump $PGDUMP_EXTRA_OPTIONS --host localhost --blobs --clean --user _pgbackup $PGDUMP_DATABASE -Fd -f $TEMPDIR/pgdump || exit 1
 
+# Dump role info
+ssh ${SSHUSER}@${HOSTNAME} "sudo -u postgres pg_dumpall -r > $TEMPDIR/pg_roles" || exit 1
+
 # Rsync to backup destination
-rsync -av --checksum --delete --no-times ${SSHUSER}@${HOSTNAME}:$TEMPDIR/pgdump/ $BACKUP_DEST
+rsync -av --checksum --delete --no-times ${SSHUSER}@${HOSTNAME}:$TEMPDIR/pgdump/ $PGDUMP_DEST
+scp ${SSHUSER}@${HOSTNAME}:$TEMPDIR/pg_roles $PGROLE_DEST
+
 # TEMPDIR will be removed on exit by tidytmp()