add option to configure cloud-init to allow password authentication

This patch will configure cloud-init to allow password authentication.
This is usefull in case you use "devuser" element and want to ssh guest
image.

Change-Id: I00e38aa2753f26b4cdd34d0fd85fc8e0de78171f

elements/cloud-init/README.rst

@@ -6,3 +6,12 @@ Install's and enables cloud-init for systems that don't come with it
 pre-installed
 
 Currently only supports Gentoo.
+
+Environment Variables
+---------------------
+
+DIB_CLOUD_INIT_ALLOW_PASS_AUTH
+  :Required: No
+  :Default: password authentication disabled when cloud-init installed
+  :Description: customize cloud-init to allow ssh password
+    authentication.

elements/cloud-init/post-install.d/21-cloud-init-allow-password-auth

@@ -0,0 +1,22 @@
+#!/bin/bash
+
+if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
+    set -x
+fi
+set -eu
+set -o pipefail
+
+# Set cloud-init to allow password authentication
+if [ -n "${DIB_CLOUD_INIT_ALLOW_SSH_PWAUTH:-}" ]; then
+    if [ -f "/etc/cloud/cloud.cfg" ]; then
+        if [ -z "$(cat /etc/cloud/cloud.cfg | grep ssh_pwauth)" ]; then
+            echo "ssh_pwauth not exist. append to EOF"
+            sudo sh -c 'echo "ssh_pwauth: 1" >> /etc/cloud/cloud.cfg'
+        else
+            echo "ssh_pwauth exist. make sure ssh_pwauth enabled"
+            sed -i -e 's/ssh_pwauth: *0/ssh_pwauth: 1/g' /etc/cloud/cloud.cfg
+            sed -i -e 's/ssh_pwauth: *False/ssh_pwauth: True/g' /etc/cloud/cloud.cfg
+            sed -i -e 's/ssh_pwauth: *false/ssh_pwauth: true/g' /etc/cloud/cloud.cfg
+        fi
+    fi
+fi