Add back unit tests with Puppet 5 + CentOS 8 Stream

This module still supports Puppet 5. This change adds back unit test
coverage with Puppet 5.

Depends-on: https://review.opendev.org/854061
Change-Id: I757d5c2f1c2af1c548d8ce6fba324c6f42826910

.zuul.yaml

@@ -5,3 +5,18 @@
       - puppet-openstack-integration-jobs-scenario001
       - puppet-openstack-integration-jobs-scenario004
       - release-notes-jobs-python3
+    check:
+      jobs:
+        - puppet-ceph-unit-5.5-centos-8-stream
+    gate:
+      jobs:
+        - puppet-ceph-unit-5.5-centos-8-stream
+- job:
+    name: puppet-ceph-unit-5.5-centos-8-stream
+    parent: puppet-openstack-unit-base
+    nodeset: centos-8-stream
+    # stable/ussuri is the last release with Puppet 5.x support
+    override-checkout: stable/ussuri
+    vars:
+      puppet_gem_version: 5.5.0
+      rspec_puppet_version: '= 2.9.0'

spec/unit/provider/ceph_config/ini_setting_spec.rb

@@ -39,11 +39,13 @@ describe provider_class do
   let(:tmpfile) { tmpfilename("ceph_config_test") }
 
   let(:params) { {
-      :path    => tmpfile,
+    :path => tmpfile,
   } }
 
   def validate(expected)
-    expect(File.read(tmpfile)).to eq(expected)
+    # NOTE(tkajinam): Remove heading \n to fix an issue with Puppet 5
+    #                 + CentOS8 Stream.
+    expect(File.read(tmpfile).gsub(/^\n/, '')).to eq(expected)
   end
 
   it 'should create keys = value and ensure space around equals' do