Update the handling of check root disk size output

Filter out the preceding blank line(s) from check root disk size
output which is intermittently included in the output when the
check_root_disk_size.py script is executed remotely with sudo.
This likely is a bug/quirk of Ansible script module. The issue
resulted in sporadic bootstrap failure during subcloud deployment.

Test Plan:
  - verify successful bootstrap of a standalone system (AIO-SX) with the change
  - verify successful bootstrap of a batch of subclouds with the change

Closes-Bug: 1995999
Signed-off-by: Tee Ngo <tee.ngo@windriver.com>
Change-Id: I7fb4780658ac3e4887cdfcde3f64b2527777bf39

playbookconfig/src/playbooks/roles/bootstrap/prepare-env/tasks/main.yml

@@ -179,7 +179,6 @@
       'system_mode': "{{ system_mode }}"
       'timezone': "{{ timezone }}"
     root_disk_size: "{{ standard_root_disk_size }}"
-    root_disk_idx: 0
     localhost_name_ip_mapping: "127.0.0.1\tlocalhost\tlocalhost.localdomain localhost4 localhost4.localdomain4"
     network_params:
       'pxeboot_subnet': "{{ pxeboot_subnet }}"
@@ -593,17 +592,48 @@
      virtual_system is defined and
      not virtual_system|bool)
 
-# Workaround an Ansible quirk
-- name: Update root disk index for remote play
+# Filter out the preceding blank line(s) from the output of remote execution
+# of check_root_disk_size.py with escalated privilege remotely - a workaround
+# for an Ansible bug/quirk.
+- name: Filter out blank lines from disk size check output
   set_fact:
-    root_disk_idx: "{{ root_disk_idx + 1 }}"
-  when: ansible_connection != "local"
+    disk_size_result: |
+      {% set disk_size_result = [] %}
+      {% for l in disk_size_check_result.stdout_lines %}
+      {% if l != "" %}
+      {% set _ = disk_size_result.append(l) %}
+      {% endif %}
+      {% endfor %}
+      {{ disk_size_result }}
+
+- debug: var=disk_size_check_result
+- debug: var=disk_size_result
+
+# The expected result, after preceding blank line(s) is filtered out, is it
+# must contain at least 2 lines, one is the root disk path and the other
+# the root disk size. For instance:
+#
+# a) if root disk size is smaller than the specified standard root disk size,
+# /dev/sdb
+# 500
+# Traceback (most recent call last):
+#   File "/usr/share/ansible/stx-ansible...."
+#       raise Exception("Failed validation!")
+#       Exception: Failed validation!
+#
+# b) if the root size is larger or equal to the specified standard root disk size:
+# /dev/sdb
+#  500
+- name: Fail if disk size check returned unexpected result
+  fail:
+    msg: "Disk size check script returned unexpected result {{ disk_size_check_result.stdout_lines }}"
+  when: (disk_size_result|length < 2 or
+         disk_size_result[1]|int == 0)
 
 - name: Set root disk and root disk size facts
   set_fact:
-    root_disk: "{{ disk_size_check_result.stdout_lines[root_disk_idx|int] }}"
-    root_disk_size: "{{ disk_size_check_result.stdout_lines[root_disk_idx|int + 1] }}"
-  failed_when: root_disk_size|int == 0
+    root_disk: "{{ disk_size_result[0] }}"
+    root_disk_size: "{{ disk_size_result[1] }}"
 
 - debug:
     msg: >-