fix some tests, split up and refactor

some wonky regression introduced by docker dependencies when running on darwin. see https://github.com/ory/dockertest/issues/212 for more info.
will have a look at this next

pkg/types/registry_credentials.go

@@ -0,0 +1,6 @@
+package types
+
+type RegistryCredentials struct {
+	Username string
+	Password string // usually a token rather than an actual password
+}

pkg/types/token_response.go

@@ -0,0 +1,5 @@
+package types
+
+type TokenResponse struct {
+	Token string `json:"token"`
+}