Enable auto-rootdisk growth on gce-backports.

This commit adds the cloud-initramfs-growroot package to the
installation list for GCE images with backports enabled, and updates
the gce tasklist to add the /etc/init.d/expand-root script
(with provider-appropriate touch-ups) to the image.

bootstrapvz/providers/gce/__init__.py

@@ -3,6 +3,7 @@ import tasks.apt
 import tasks.boot
 import tasks.configuration
 import tasks.image
+import tasks.initd
 import tasks.host
 import tasks.packages
 from bootstrapvz.common.tasks import apt
@@ -31,6 +32,7 @@ def resolve_tasks(taskset, manifest):
 	                tasks.apt.SetPackageRepositories,
 	                tasks.apt.ImportGoogleKey,
 	                tasks.packages.DefaultPackages,
+	                tasks.packages.ReleasePackages,
 	                tasks.packages.GooglePackages,
 
 	                tasks.configuration.GatherReleaseInformation,
@@ -38,6 +40,8 @@ def resolve_tasks(taskset, manifest):
 	                tasks.host.DisableIPv6,
 	                tasks.host.InstallHostnameHook,
 	                tasks.boot.ConfigureGrub,
+	                initd.AddExpandRoot,
+	                tasks.initd.AdjustExpandRootDev,
 	                initd.InstallInitScripts,
 	                ssh.AddSSHKeyGeneration,
 	                ssh.DisableSSHPasswordAuthentication,
@@ -48,6 +52,9 @@ def resolve_tasks(taskset, manifest):
 	                volume.Delete,
 	                ])
 
+	if manifest.volume['partitions']['type'] != 'none':
+		taskset.add(initd.AdjustExpandRootScript)
+
 	if 'gcs_destination' in manifest.image:
 		taskset.add(tasks.image.UploadImage)
 		if 'gce_project' in manifest.image:

bootstrapvz/providers/gce/tasks/initd.py

@@ -0,0 +1,16 @@
+from bootstrapvz.base import Task
+from bootstrapvz.common import phases
+from bootstrapvz.common.tasks import initd
+
+
+class AdjustExpandRootDev(Task):
+	description = 'Adjusting the expand-root device'
+	phase = phases.system_modification
+	predecessors = [initd.AddExpandRoot, initd.AdjustExpandRootScript]
+
+	@classmethod
+	def run(cls, info):
+		import os.path
+		from bootstrapvz.common.tools import sed_i
+		script = os.path.join(info.root, 'etc/init.d/expand-root')
+		sed_i(script, '/dev/xvda', '/dev/sda')

bootstrapvz/providers/gce/tasks/packages.py

@@ -1,6 +1,7 @@
 from bootstrapvz.base import Task
 from bootstrapvz.common import phases
 from bootstrapvz.common.tasks import apt
+import logging
 import os
 
 
@@ -28,6 +29,21 @@ class DefaultPackages(Task):
 		info.packages.add(kernel_package)
 
 
+class ReleasePackages(Task):
+	description = 'Adding release-specific packages required for GCE'
+	phase = phases.preparation
+	predecessors = [apt.AddDefaultSources, apt.AddBackports, DefaultPackages]
+
+	@classmethod
+	def run(cls, info):
+		# Add release-specific packages, if available.
+		if info.source_lists.target_exists('wheezy-backports'):
+			info.packages.add('cloud-initramfs-growroot')
+		else:
+			msg = ('No release-specific packages found for {system.release}').format(**info.manifest_vars)
+			logging.getLogger(__name__).warning(msg)
+
+
 class GooglePackages(Task):
 	description = 'Adding image packages required for GCE from Google repositories'
 	phase = phases.preparation