POSIX: Changed px4_debug.h to px4_log.h

Also changed use of printf to PX4_WARN or PX4_INFO in posix and
qurt tests.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/platforms/qurt/tests/hello/hello_example.cpp

@@ -1,4 +1,3 @@
-
 /****************************************************************************
  *
  *   Copyright (C) 2015 Mark Charlebois. All rights reserved.
@@ -40,6 +39,7 @@
  */
 
 #include "hello_example.h"
+#include <px4_log.h>
 #include <unistd.h>
 #include <stdio.h>
 
@@ -52,7 +52,7 @@ int HelloExample::main()
 	int i=0;
 	while (!appState.exitRequested() && i<5) {
 
-		printf("  Doing work...\n");
+		PX4_DEBUG("  Doing work...\n");
 		++i;
 	}