Treat SIGTERM as a server disconnect signal (#2580)

Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

cmd/dlv/cmds/commands.go

@@ -690,14 +690,14 @@ func connectCmd(cmd *cobra.Command, args []string) {
 }
 
 // waitForDisconnectSignal is a blocking function that waits for either
-// a SIGINT (Ctrl-C) signal from the OS or for disconnectChan to be closed
-// by the server when the client disconnects.
+// a SIGINT (Ctrl-C) or SIGTERM (kill -15) OS signal or for disconnectChan
+// to be closed by the server when the client disconnects.
 // Note that in headless mode, the debugged process is foregrounded
 // (to have control of the tty for debugging interactive programs),
 // so SIGINT gets sent to the debuggee and not to delve.
 func waitForDisconnectSignal(disconnectChan chan struct{}) {
 	ch := make(chan os.Signal, 1)
-	signal.Notify(ch, syscall.SIGINT)
+	signal.Notify(ch, syscall.SIGINT, syscall.SIGTERM)
 	if runtime.GOOS == "windows" {
 		// On windows Ctrl-C sent to inferior process is delivered
 		// as SIGINT to delve. Ignore it instead of stopping the server