Add priority to the EmbeddedAnsible subclasses

This sorts the subclasses and instantiates the first available one

lib/embedded_ansible.rb

@@ -10,7 +10,7 @@ def self.new
   end
 
   def self.detect_available_platform
-    subclasses.detect(&:available?) || NullEmbeddedAnsible
+    subclasses.sort.detect(&:available?) || NullEmbeddedAnsible
   end
 
   def self.available?
@@ -21,6 +21,14 @@ def self.enabled?
     MiqServer.my_server(true).has_active_role?(ANSIBLE_ROLE)
   end
 
+  def self.priority
+    0
+  end
+
+  def self.<=>(other_embedded_ansible)
+    other_embedded_ansible.priority <=> priority
+  end
+
   def alive?
     return false unless configured? && running?
     begin

lib/embedded_ansible/appliance_embedded_ansible.rb

@@ -18,6 +18,10 @@ def self.available?
     required_rpms.subset?(LinuxAdmin::Rpm.list_installed.keys.to_set)
   end
 
+  def self.priority
+    30
+  end
+
   def initialize
     require "linux_admin"
   end

lib/embedded_ansible/container_embedded_ansible.rb

@@ -5,6 +5,10 @@ def self.available?
     ContainerOrchestrator.available?
   end
 
+  def self.priority
+    20
+  end
+
   def start
     miq_database.set_ansible_admin_authentication(:password => ENV["ANSIBLE_ADMIN_PASSWORD"])
     ContainerOrchestrator.new.scale(ANSIBLE_DC_NAME, 1)

lib/embedded_ansible/docker_embedded_ansible.rb

@@ -8,6 +8,10 @@ def self.available?
     false
   end
 
+  def self.priority
+    10
+  end
+
   def initialize
     super
     require 'docker'

spec/lib/embedded_ansible_spec.rb

@@ -1,6 +1,12 @@
 require 'docker'
 
 describe EmbeddedAnsible do
+  describe ".<=>" do
+    it "allows classes to be sorted by priority" do
+      expect(EmbeddedAnsible.subclasses.sort).to eq([ApplianceEmbeddedAnsible, ContainerEmbeddedAnsible, DockerEmbeddedAnsible, NullEmbeddedAnsible])
+    end
+  end
+
   context "with no available subclass" do
     before do
       expect(MiqEnvironment::Command).to receive(:is_appliance?).and_return(false)