Implement basic Remote::Environment class:

Represent a registry for remote environment variables, will follow an
API similar to Hash except the constructor. Currently only #has_key? is
implemented.

spec/producer/core/remote/environment_spec.rb

@@ -0,0 +1,34 @@
+require 'spec_helper'
+
+module Producer::Core
+  describe Remote::Environment do
+    let(:variables)       { { 'FOO' => 'bar', 'BAZ' => 'qux' } }
+    subject(:environment) { Remote::Environment.new(variables) }
+
+    describe '#initialize' do
+      context 'when a hash is given' do
+        it 'assigns the key/value pairs' do
+          expect(environment.instance_eval { @variables }).to eq variables
+        end
+      end
+
+      context 'when a string is given' do
+        subject(:environment) { Remote::Environment.new("FOO=bar\nBAZ=qux") }
+
+        it 'assigns the key/value pairs' do
+          expect(environment.instance_eval { @variables }).to eq variables
+        end
+      end
+    end
+
+    describe '#has_key?' do
+      let(:key) { 'SOME_KEY' }
+
+      it 'forwards the message to @variables' do
+        expect(environment.instance_eval { @variables })
+          .to receive(:has_key?).with(key)
+        environment.has_key? key
+      end
+    end
+  end
+end