Enable cloud-init apt-configure module for Azure stemcells

Azure stemcells now properly use Azure-optimized APT mirrors
(azure.archive.ubuntu.com) by enabling the apt-configure module
in cloud-init configuration.

The LISA (Linux Integration Services Automation) test suite's
verify_repository_installed test was failing because Azure VMs
were using archive.ubuntu.com instead of azure.archive.ubuntu.com
for APT package repositories. While the Azure mirror configuration
existed in /etc/cloud/cloud.cfg.d/90-azure-apt-sources.cfg, it
was never applied because the apt-configure module was not enabled
in cloud-init's module list.

Added apt-configure to the cloud_init_modules list in cloud.cfg,
which instructs cloud-init to read and apply the Azure APT mirror
configuration at VM boot time. This ensures /etc/apt/sources.list
is automatically updated to use Azure-optimized mirrors.

Author: s4heid

bosh-stemcell/spec/stemcells/azure_spec.rb

@@ -43,6 +43,18 @@
     end
   end
 
+  context 'cloud-init Azure APT mirror configuration' do
+    describe file('/etc/cloud/cloud.cfg.d/90-azure-apt-sources.cfg') do
+      it { should be_file }
+      its(:content) { should include('http://azure.archive.ubuntu.com/ubuntu/') }
+    end
+
+    describe file('/etc/cloud/cloud.cfg') do
+      it { should be_file }
+      its(:content) { should include('apt-configure') }
+    end
+  end
+
   context 'installed by system_azure_network', {
     exclude_on_alicloud: true,
     exclude_on_aws: true,

stemcell_builder/stages/system_azure_init/assets/etc/cloud-init/cloud.cfg

@@ -10,6 +10,7 @@ cloud_init_modules:
  - update_etc_hosts
  - users-groups
  - ssh
+ - apt-configure
 cloud_config_modules:
  - ssh-import-id
  - set-passwords