Tools: Fix exim configuration for non-local addresses

exim evaluates the available routers in order; as in the Tools
configuration the dnslookup router comes last, this means that for
addresses with local parts that are valid usernames in Labs or match
the patterns for tool accounts, messages are delivered to the "local"
user instead of the intended recipient:

| root@tools-mail:~# exim -bt legoktm@tim-landscheidt.de
| legoktm.wikipedia@gmail.com
|     <-- legoktm@tim-landscheidt.de
|   router = dnslookup, transport = remote_smtp
|   host gmail-smtp-in.l.google.com      [2607:f8b0:4001:c05::1b] MX=5
|   host gmail-smtp-in.l.google.com      [74.125.193.26]          MX=5
|   host alt1.gmail-smtp-in.l.google.com [2607:f8b0:400d:c00::1b] MX=10
|   host alt1.gmail-smtp-in.l.google.com [173.194.68.26]          MX=10
|   host alt2.gmail-smtp-in.l.google.com [2607:f8b0:400c:c03::1a] MX=20
|   host alt2.gmail-smtp-in.l.google.com [74.125.131.26]          MX=20
|   host alt3.gmail-smtp-in.l.google.com [2a00:1450:400c:c05::1a] MX=30
|   host alt3.gmail-smtp-in.l.google.com [173.194.67.26]          MX=30
|   host alt4.gmail-smtp-in.l.google.com [2a00:1450:4013:c01::1a] MX=40
|   host alt4.gmail-smtp-in.l.google.com [74.125.136.27]          MX=40
| root@tools-mail:~#

This change puts the dnslookup router at the top like in the default
configuration, so that non-local addresses are handled properly while
not changing the behaviour for local addresses:

| root@tools-mail:~# exim -C /etc/exim4/exim4-bug-68545.conf -bt legoktm@tim-landscheidt.de
| legoktm@tim-landscheidt.de
|   router = dnslookup, transport = remote_smtp
|   host smtp.rzone.de [2a01:238:20a:202:50f0::2097] MX=5
|   host smtp.rzone.de [81.169.145.98]               MX=5
| root@tools-mail:~# exim -C /etc/exim4/exim4-bug-68545.conf -bt legoktm@tools.wmflabs.org
| legoktm.wikipedia@gmail.com
|     <-- legoktm@tools.wmflabs.org
|   router = dnslookup, transport = remote_smtp
|   host gmail-smtp-in.l.google.com      [2607:f8b0:4001:c05::1b] MX=5
|   host gmail-smtp-in.l.google.com      [74.125.193.26]          MX=5
|   host alt1.gmail-smtp-in.l.google.com [2607:f8b0:400d:c00::1a] MX=10
|   host alt1.gmail-smtp-in.l.google.com [173.194.68.26]          MX=10
|   host alt2.gmail-smtp-in.l.google.com [2607:f8b0:400c:c03::1a] MX=20
|   host alt2.gmail-smtp-in.l.google.com [74.125.131.27]          MX=20
|   host alt3.gmail-smtp-in.l.google.com [2a00:1450:400c:c05::1a] MX=30
|   host alt3.gmail-smtp-in.l.google.com [173.194.67.26]          MX=30
|   host alt4.gmail-smtp-in.l.google.com [2a00:1450:4013:c01::1a] MX=40
|   host alt4.gmail-smtp-in.l.google.com [74.125.136.27]          MX=40
| root@tools-mail:~#

Bug: 68545
Change-Id: I802915038e9edf2803712f62a5854f4e64b12ca3
Merge "Tools: Fix exim configuration for non-local addresses" into production