adding /__admin/stop endpoint for httpserver

[chaudharydeepak]

#1571

Adding endpoint to shutdown the server.

• Relevant Issues : GET requests to path '__admin/stop' no longer stop a mock server #1571 Adding endpoint to shutdown the server.
• Relevant PRs :
• Type of change :
  • Bug fix for existing feature

[chaudharydeepak]

@ptrthomas - let me know if this looks ok. I added the functionality to com.intuit.karate.http.HttpServer. also we are not checking for METHOD, we can enforce POST only. Http Response is 202 ACCEPTED vs 200. Thank you.