Add a programatic way to exit linkerd-tcp (#24)

Problem:

Some profiling tools are not well suited for long running server
processes and rely on the process exiting to finish their work.

Solution:

POST /quitquitquit is an out-of-band signal for exiting the process. POST
is used to prevent accidental curling (which uses GET by default) or
web browsing from exiting the process.

Author: stevej

src/app/admin_http.rs

@@ -1,9 +1,10 @@
 use futures::{Future, future};
-use hyper::{self, Get, StatusCode};
+use hyper::{self, Get, Post, StatusCode};
 use hyper::header::ContentLength;
 use hyper::server::{Service, Request, Response};
 use std::boxed::Box;
 use std::cell::RefCell;
+use std::process;
 use std::rc::Rc;
 
 pub struct Server {
@@ -43,6 +44,9 @@ impl Service for Server {
                     })
                     .boxed()
             }
+            (&Post, "/shutdown") => {
+                process::exit(0);
+            }
             _ => future::ok(Response::new().with_status(StatusCode::NotFound)).boxed(),
         }
     }