add apt_reboot_if_required to reboot if required

If an upgrade or package installation forced a reboot (such as a kernel
upgrade), then we can optionally reboot at that point.

This allows the user to not be into the newest available kernel without
needing a reboot on their own.

ChangeLog

@@ -1,4 +1,6 @@
 0.7.0:
+ - add apt_reboot_if_required to reboot if an upgrade or package installation
+   forced the need for one (LP: #1038108)
  - allow distro mirror selection to include availability-zone (LP: #1037727)
  - allow arch specific mirror selection (select ports.ubuntu.com on arm)
    LP: #1028501

cloudinit/config/cc_apt_update_upgrade.py

@@ -20,6 +20,7 @@
 
 import glob
 import os
+import time
 
 from cloudinit import templater
 from cloudinit import util
@@ -125,6 +126,20 @@ def handle(name, cfg, cloud, log, _args):
             util.logexc(log, "Failed to install packages: %s ", pkglist)
             errors.append(e)
 
+    # kernel and openssl (possibly some other packages)
+    # write a file /var/run/reboot-required after upgrading.
+    # if that file exists and configured, then just stop right now and reboot
+    # TODO(smoser): handle this less voilently
+    reboot_file = "/var/run/reboot-required"
+    if ((upgrade or pkglist) and cfg.get("apt_reboot_if_required", False) and
+         os.path.isfile(reboot_file)):
+        log.warn("rebooting after upgrade or install per %s" % reboot_file)
+        time.sleep(1)  # give the warning time to get out
+        util.subp(["/sbin/reboot"])
+        time.sleep(60)
+        log.warn("requested reboot did not happen!")
+        errors.append(Exception("requested reboot did not happen!"))
+
     if len(errors):
         log.warn("%s failed with exceptions, re-raising the last one",
                  len(errors))