scripts: Add Ubuntu cloud-init data

Add cloud-init data for Ubuntu and introduce a convenience script that
can be used to generate cloud-init disk images for manual testing.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

test_data/cloud-init/ubuntu/meta-data

@@ -0,0 +1,2 @@
+instance-id: cloud
+local-hostname: cloud

test_data/cloud-init/ubuntu/network-config

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+network:
+  version: 1
+  config:
+    - type: physical
+      name: eth0
+      mac_address: 12:34:56:78:90:ab
+      subnets:
+         - type: static
+           address: 192.168.2.2/24
+           gateway: 192.168.2.1
+           dns_nameservers:
+              - 192.168.2.1

test_data/cloud-init/ubuntu/user-data

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+#cloud-config
+users:
+  - name: cloud
+    passwd: $6$7125787751a8d18a$sHwGySomUA1PawiNFWVCKYQN.Ec.Wzz0JtPPL1MvzFrkwmop2dq7.4CYf03A5oemPQ4pOFCCrtCelvFBEle/K.
+    sudo: ALL=(ALL) NOPASSWD:ALL
+    lock_passwd: False
+    inactive: False
+    shell: /bin/bash
+
+ssh_pwauth: True