upstart/cloud-init-nonet.conf: handle SIGTERM gracefully

this fixes a confusing message, most commonly found in /var/log/dmesg
or seen on log screens:
   init: cloud-init-nonet main process (307) killed by TERM signal

This was actually *expected* as the upstart job was supposed to block
until networking came up, and the SIGTERM was sent by upstart.

That said, the message was confusing.  Now, instead we will see something like
  cloud-init-nonet[6.54]: waiting 10 seconds for network device
  cloud-init-nonet[12.13]: static networking is now up

Which is much nicer.  In the event that networking does not come up
you'll see:
  cloud-init-nonet[X.Y]: gave up waiting for a network device.

LP: #1015223

1 files changed, 47 insertions, 11 deletions

diff --git a/upstart/cloud-init-nonet.conf b/upstart/cloud-init-nonet.conf
index 118ffc1c..36b99fb5 100644
--- a/upstart/cloud-init-nonet.conf
+++ b/upstart/cloud-init-nonet.conf
@@ -10,19 +10,55 @@ task
 console output
 
 script
-   # /run/network/static-network-up-emitted is written by
-   # upstart (via /etc/network/if-up.d/upstart). its presense would
-   # indicate that static-network-up has already fired.
-	EMITTED="/run/network/static-network-up-emitted"
-   [ -e "$EMITTED" -o -e "/var/$EMITTED" ] && exit 0
+   set +e  # you cannot trap TERM reliably with 'set -e'
+   SLEEP_CHILD=""
 
+   static_network_up() {
+	   local emitted="/run/network/static-network-up-emitted"
+      # /run/network/static-network-up-emitted is written by
+      # upstart (via /etc/network/if-up.d/upstart). its presense would
+      # indicate that static-network-up has already fired.
+      [ -e "$emitted" -o -e "/var/$emitted" ]
+   }
+   msg() {
+      local uptime="" idle=""
+      if [ -r /proc/uptime ]; then
+         read uptime idle < /proc/uptime
+      fi
+      echo "$UPSTART_JOB${uptime:+[${uptime}]}:" "$1"
+   }
+
+   handle_sigterm() {
+      # if we received sigterm and static networking is up then it probably
+      # came from upstart as a result of 'stop on static-network-up'
+      [ -z "$SLEEP_CHILD" ] || kill $SLEEP_CHILD
+      if static_network_up; then
+         msg "static networking is now up"
+         exit 0
+      fi
+      msg "recieved SIGTERM, networking not up"
+      exit 2
+   }
+
+   dowait() {
+      msg "waiting $1 seconds for network device"
+      sleep "$1" &
+      SLEEP_CHILD=$!
+      wait $SLEEP_CHILD
+      SLEEP_CHILD=""
+   }
+
+   trap handle_sigterm TERM
+
+   # static_network_up already occurred
+   static_network_up && exit 0
+
+   # obj.pkl comes from cloud-init-local (or previous boot and
+   # manual_cache_clean)
    [ -f /var/lib/cloud/instance/obj.pkl ] && exit 0
 
-   short=10; long=120;
-   sleep ${short}
-   echo $UPSTART_JOB "waiting ${long} seconds for a network device."
-   sleep ${long}
-   echo $UPSTART_JOB "gave up waiting for a network device."
+   dowait 10
+   dowait 120
+   msg "gave up waiting for a network device."
    : > /var/lib/cloud/data/no-net
 end script
-# EOF