Created container.h and added more comprehensive hello world

Added a per-container container.h that inclues useful definitions.
Hello world now is in a separate file not to modify main too often.
hello world now prints container name and id.

conts/test/hello.c

@@ -0,0 +1,13 @@
+/*
+ * Autogenerated hello world print function
+ */
+
+#include <stdio.h>
+#include <container.h>
+
+int print_hello_world(void)
+{
+	printf("%s: Hello world from %s!\n", __CONTAINER__, __CONTAINER_NAME__);
+	return 0;
+}
+