change tests to fit more inline with repo current way of testing

- separate redirect + redirect interpolation changes
- use env hash inside test and don't hardcode in app_runner.rb

spec/fixtures/redirects/static.json

@@ -3,10 +3,6 @@
     "/old/gone": {
       "url": "/",
       "status": 302
-    },
-    "/old/interpolation": {
-      "url": "${INTERPOLATED_URL}",
-      "status": 302
     }
   }
 }

spec/fixtures/redirects_interpolation/public_html/index.html

+hello world

spec/fixtures/redirects_interpolation/static.json

+{
+  "redirects": {
+    "/old/gone": {
+      "url": "/",
+      "status": 302
+    },
+    "/old/interpolation": {
+      "url": "${INTERPOLATED_URL}",
+      "status": 302
+    }
+  }
+}

spec/simple_spec.rb

@@ -90,12 +90,20 @@ RSpec.describe "Simple" do
       expect(response["location"]).to eq("http://#{AppRunner::HOST_IP}/")
     end
 
+    context "interpolation" do
+      let(:name) { "redirects_interpolation" }
+
+      let(:env)  {
+        { "INTERPOLATED_URL" => "/interpolation.html" }
+      }
+
       it "should redirect using interpolated urls" do
         response = app.get("/old/interpolation")
         expect(response.code).to eq("302")
         expect(response["location"]).to eq("http://#{AppRunner::HOST_IP}/interpolation.html")
       end
     end
+  end
 
   describe "https only" do
     let(:name) { "https_only" }

spec/support/app_runner.rb

@@ -24,9 +24,6 @@ class AppRunner
     @debug     = debug
     env.merge!("STATIC_DEBUG" => true) if @debug
 
-    # support interpolation specs
-    env.merge!("INTERPOLATED_URL" => "/interpolation.html")
-
     @container = Docker::Container.create(
       "Image"      => BuildpackBuilder::TAG,
       "Cmd"        => ["bash", "-c", "cp -rf /src/* /app/ && /app/bin/boot"],