Fix a bug in the move-machine script

The generation of the command to unexport NFS filesystems could generate
an invalid command. Leading spaces were not being stripped, and in cases
where there is more than one backup target for a machine we need to
unexport every target. Because we also had 'set -e' in operation at this
point, the script would fail there and never clean up the moved ZFS. I
don't mind if we fail to unexport; if that's subsequently a problem for
removing the ZFS then the script will fail at that point.

This change makes the script generate better exportfs -u commands and
not exit if they fail.

ROOT/DEBIAN/control

@@ -3,6 +3,6 @@ Priority: optional
 Section: otherosfs
 Maintainer: Chemistry COs <support@ch.cam.ac.uk>
 Architecture: all
-Version: 0.9-ch75
+Version: 0.9-ch76
 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/move-machine.sh

@@ -71,8 +71,12 @@ echo Re-enabling backup task
 dosql "update host set disabled='f' where hostname='$FQDN';"
 # Tidy up
 echo Removing old ZFS, snapshots etc
-# need to unexport nfs here
-EXPORT=`dosql "select zfs_target from backup_task where backup_task_id in (select backup_task_id from backup_task natural join host where hostname='$FQDN')"`
-exportfs -u $FQDN:/$EXPORT
+# need to try to unexport nfs here, but failure isn't a worry
+set +e
+EXPORTS=`dosql "select zfs_target from backup_task where backup_task_id in (select backup_task_id from backup_task natural join host where hostname='$FQDN')"`
+for EXPORT in $EXPORTS ; do
+  exportfs -u $FQDN:/$EXPORT
+done
+set -e
 for SN in `zfs list -r -t snapshot -H -o name $SOURCE/$FQDN ` ; do for H in `zfs holds -H $SN | awk ' { print $2 ; } '` ; do zfs release $H $SN ; done ; done
 zfs destroy -r $SOURCE/$FQDN