(POOLER-70) Add config for VM Provider

This commit adds a public function to access the internal variable holding the
VMPooler configuration.  This is required for later commits for the execute!
function testing.

spec/unit/pool_manager_spec.rb

@@ -36,6 +36,16 @@ EOT
 
   subject { Vmpooler::PoolManager.new(config, logger, redis, metrics) }
 
+  describe '#config' do
+    before do
+      expect(subject).not_to be_nil
+    end
+
+    it 'should return the current configuration' do
+      expect(subject.config).to eq(config)
+    end
+  end
+
   describe '#check_pending_vm' do
     before do
       expect(subject).not_to be_nil