Enable frozen string across project (#1319)

Turn on frozen string support in all files by using a comment to avoid
enabling across dependencies where it may not work.

Fixes: #1177

spec/support/binding_proc.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 ##
 # A simple extension of the Proc class that supports setting a custom binding
 # and evaluates everything in the Proc using the new binding.

spec/support/environment_helper.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'ostruct'
 require 'pathname'
 

spec/support/libvirt_context.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'fog/libvirt'
 
 shared_context 'libvirt' do

spec/support/matchers/have_file_content.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "rspec/expectations/version"
 #
 # Taken from https://github.com/cucumber/aruba/blob/main/lib/aruba/matchers/file/have_file_content.rb

spec/support/sharedcontext.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'spec_helper'
 
 shared_context 'unit' do

spec/support/temporary_dir.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 shared_context 'temporary_dir' do
   around do |example|
     Dir.mktmpdir("rspec-") do |dir|