(POOLER-143) Add clone_target config change to API

This allows the user to change the cluster in which the targeted pool
will clone to. Upon configuration change, the thread will wake up and
execute the change within 1 second.

spec/integration/api/v1/config_spec.rb

@@ -16,7 +16,7 @@ describe Vmpooler::API::V1 do
         'experimental_features' => true
       },
       pools: [
-        {'name' => 'pool1', 'size' => 5, 'template' => 'templates/pool1'},
+        {'name' => 'pool1', 'size' => 5, 'template' => 'templates/pool1', 'clone_target' => 'default_cluster'},
         {'name' => 'pool2', 'size' => 10}
       ],
       statsd: { 'prefix' => 'stats_prefix'},
@@ -223,6 +223,69 @@ describe Vmpooler::API::V1 do
       end
     end
 
+    describe 'POST /config/clonetarget' do
+      it 'changes the clone target' do
+        post "#{prefix}/config/clonetarget", '{"pool1":"cluster1"}'
+        expect_json(ok = true, http = 201)
+
+        expected = { ok: true }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+      end
+
+      it 'changes a pool size for multiple pools' do
+        post "#{prefix}/config/clonetarget", '{"pool1":"cluster1","pool2":"cluster2"}'
+        expect_json(ok = true, http = 201)
+
+        expected = { ok: true }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+      end
+
+      it 'fails when a specified pool does not exist' do
+        post "#{prefix}/config/clonetarget", '{"pool10":"cluster1"}'
+        expect_json(ok = false, http = 400)
+        expected = {
+          ok: false,
+          bad_templates: ['pool10']
+        }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+      end
+
+      it 'succeeds with 200 when no change is required' do
+        post "#{prefix}/config/clonetarget", '{"pool1":"default_cluster"}'
+        expect_json(ok = true, http = 200)
+
+        expected = { ok: true }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+      end
+
+      it 'succeeds with 201 when at least one pool changes' do
+        post "#{prefix}/config/clonetarget", '{"pool1":"default_cluster","pool2":"cluster2"}'
+        expect_json(ok = true, http = 201)
+
+        expected = { ok: true }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+      end
+
+      context 'with experimental features disabled' do
+        before(:each) do
+          config[:config]['experimental_features'] = false
+        end
+
+        it 'should return 405' do
+          post "#{prefix}/config/clonetarget", '{"pool1":"cluster1"}'
+          expect_json(ok = false, http = 405)
+
+          expected = { ok: false }
+          expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        end
+      end
+    end
+
     describe 'GET /config' do
       let(:prefix) { '/api/v1' }