Use CreateExternalDefaultClient rather than CreateDefaultClient for

the tarballProvider http client

This was probably fine before on accident. The internal client only
has a few ciphers enabled and now that bionic stemcells are hosted
on storage.googleapis.com this was causing the following error:

remote error: tls: handshake failure

cmd/env_factory.go

@@ -90,7 +90,7 @@ func NewEnvFactory(
 	{
 		tarballCacheBasePath := filepath.Join(workspaceRootPath, "downloads")
 		tarballCache := bitarball.NewCache(tarballCacheBasePath, deps.FS, deps.Logger)
-		httpClient := httpclient.NewHTTPClient(httpclient.CreateDefaultClient(nil), deps.Logger)
+		httpClient := httpclient.NewHTTPClient(httpclient.CreateExternalDefaultClient(nil), deps.Logger)
 		tarballProvider := bitarball.NewProvider(
 			tarballCache, deps.FS, httpClient, 3, 500*time.Millisecond, deps.Logger)
 

installation/tarball/provider_test.go

@@ -35,7 +35,7 @@ var _ = Describe("Provider", func() {
 		fs = fakesys.NewFakeFileSystem()
 		logger := boshlog.NewLogger(boshlog.LevelNone)
 		cache = NewCache(filepath.Join("/", "fake-base-path"), fs, logger)
-		httpClient := httpclient.NewHTTPClient(httpclient.DefaultClient, logger)
+		httpClient := httpclient.NewHTTPClient(httpclient.CreateExternalDefaultClient(nil), logger)
 		provider = NewProvider(cache, fs, httpClient, 3, 0, logger)
 		fakeStage = fakebiui.NewFakeStage()
 	})