Divert out/err streams while command runs

Actually System.in works fine, it's the output streams that get buffered.
We can fix it by diverting them for the duration of the command.

Fixes gh-217

spring-boot-cli/src/main/java/org/springframework/boot/cli/command/ShellCommand.java

@@ -159,7 +159,7 @@ public class ShellCommand extends AbstractCommand {
 					launchProcess(args, systemOut, systemErr);
 				}
 				else {
-					runCommand(args);
+					runCommand(args, systemOut, systemErr);
 				}
 			}
 		}
@@ -238,9 +238,20 @@ public class ShellCommand extends AbstractCommand {
 		ReflectionUtils.invokeMethod(PROCESS_BUILDER_INHERIT_IO_METHOD, processBuilder);
 	}
 
-	private void runCommand(List<String> args) {
+	private void runCommand(List<String> args, PrintStream systemOut,
+			PrintStream systemErr) {
 		if (!getName().equals(args.get(0))) {
-			this.springCli.runAndHandleErrors(args.toArray(new String[args.size()]));
+			PrintStream out = System.out;
+			PrintStream err = System.err;
+			System.setOut(systemOut);
+			System.setErr(systemErr);
+			try {
+				this.springCli.runAndHandleErrors(args.toArray(new String[args.size()]));
+			}
+			finally {
+				System.setOut(out);
+				System.setErr(err);
+			}
 		}
 	}