Allow the user to define PKs at the host-level (align with the docs)

lib/electric_sheep/interactors/ssh_interactor.rb

@@ -51,11 +51,15 @@ def build_session
           @host.hostname,
           @user,
           port: @host.ssh_port,
-          key_data: Crypto.get_key(@project.private_key, :private).export,
+          key_data: Crypto.get_key(private_key, :private).export,
           keys_only: true
         )
       end
 
+      def private_key
+        @host.private_key || @project.private_key
+      end
+
     end
   end
 end

lib/electric_sheep/metadata/hosts.rb

@@ -15,6 +15,7 @@ class Host < BaseHost
       option :hostname, required: true
       option :ssh_port
       option :description
+      option :private_key
 
       def initialize(options={})
         options[:ssh_port] ||= 22

spec/electric_sheep/interactors/ssh_interactor_spec.rb

@@ -56,6 +56,24 @@ def exchange_keys
     Net::SSH::Test.remove_io_aliases
   end
 
+  describe 'selecting the private key' do
+
+    let(:host){ mock }
+    let(:project){ mock }
+
+    it 'uses the host key if specified' do
+      host.expects(:private_key).returns('key_rsa')
+      subject.new(host, project, 'user').send(:private_key).must_equal 'key_rsa'
+    end
+
+    it 'falls back to the project key' do
+      host.expects(:private_key).returns(nil)
+      project.expects(:private_key).returns('key_rsa')
+      subject.new(host, project, 'user').send(:private_key).must_equal 'key_rsa'
+    end
+
+  end
+
   describe "with a session" do
 
     def build_ssh_story(cmd, replies={}, exit_status=0)

spec/electric_sheep/metadata/hosts_spec.rb

@@ -4,16 +4,18 @@
   include Support::Options
 
   it{
-    defines_options :hostname, :id, :description, :ssh_port
+    defines_options :hostname, :id, :description, :ssh_port, :private_key
     requires :hostname
   }
+
   it 'is remote' do
     subject.new.local?.must_equal false
   end
 
-  it 'use its id when converting to string' do
+  it 'uses its id when converting to string' do
     subject.new(id: 'some-id').to_s.must_equal 'some-id'
   end
+
 end
 
 describe ElectricSheep::Metadata::Localhost do