t/cmd/lfstest-gitserver.go: close test servers

The lfstest-gitserver utility program used by our test suite to
simulate a full Git LFS server starts a multiple HTTP server
instances using the implementation provided by the Go language's
"net/http/httptest" package.

However, these server instances are never cleanly shut down, and while
this makes no difference to the success of our test suite, the Go
documentation advises that we should call the Close() method for
each Server structure, so we do that now after the primary server
receives a request to its "/shutdown" endpoint.

We also adjust the message logged by the program upon shutdown so
it is no longer prefixed with "init" but rather "close".

Author: chrisd8088

t/cmd/lfstest-gitserver.go

@@ -156,7 +156,10 @@ func main() {
 	debug("init", "server client cert url: %s", serverClientCert.URL)
 
 	<-stopch
-	debug("init", "git server done")
+	server.Close()
+	serverTLS.Close()
+	serverClientCert.Close()
+	debug("close", "git server done")
 }
 
 // writeTestStateFile writes contents to either the file referenced by the