Tidy global_ignore - remove some long-since unneeded lines that should have been host-specific in the first place

e.g. /DATA for apps, /home/web for atm webserver. Also /run was in twice...

Our backup logs are generally full of

+ ssh -p 22 -o ConnectTimeout=10 root@openvpn2020.ch.cam.ac.uk '
  umask 077
  FILELIST=`tempfile`
  CONFLIST=`tempfile`
  mkdir -p /var/adm/backup
  # Make logrotate use datestamps
  if ! grep -q dateext /etc/logrotate.conf ; then sed  -i '\''s/^include/dateext\ninclude/'\'' /etc/logrotate.conf ; fi
  # Which packages are installed?
  dpkg --get-selections | awk '\'' { print $1 ; } '\'' >/var/adm/backup/packages
  cat /var/lib/dpkg/info/*.list | while read F ; do [ -f "$F" ] && echo "$F" ; done | sort > $FILELIST
  awk '\''/Description:/ { flag = 0 } ; flag == 1 { print $1 ; }  ; /Conffiles:/ { flag = 1  } ; '\'' </var/lib/dpkg/status |  sort >$CONFLIST
  diff -u $FILELIST $CONFLIST | grep ^-/ | sed s/^-// >/var/adm/backup/package-files
  rm
 '
rm: missing operand

because we're not escaping the args to that final rm command! This means we gradually fill
up /tmp, especially on machines that are infrequently rebooted (e.g. calculon)

From the comment in the script, I think this was an attempt to ignore an
error about setting GIDs. The only place I saw that particular error
occuring in practice was for loopback-mounted isos on OS builders.
We shouldn't be backing those up in the first place! Exit code
23 is "partial transfer due to error" and so can be due to problems
other than failing to set GIDs

Previously just depended on 'postgres' which was OK until we switched to
using the Postgres provided repository for postgres packages, which
makes postgres be postgres 10. Haven't tested any of the infrastructure
for 10 and don't want to start right now.

prepare-olddebian : does not do package file excludes
prepare-database: does not do package file excludes or dump databases

These are for use on machines where we can no longer reinstate them by
quickly and easily installing a new VM from the network and then
layering the backup on top, usually because the OS is obsolete.

The script runs some SQL which ultimately determines the time at which the last
backup with an exit code of zero was. If there has never been a successful
backup, we ended up reporting a clear dot. Whilst this may lead to a few
transitory red dots immediately after adding a new host, I think this is
preferable to not realising for months that a host isn't being backed up!
See ticket 154527

For offline machines, use the time between last backup and last change of conn dot status to decide on backup status