Add some testcases and examples for value override operator.
Link: https://lkml.kernel.org/r/159482883824.126704.2166030493721357163.stgit@devnote2
Signed-off-by: Masami Hiramatsu Signed-off-by: Steven Rostedt (VMware)
key = value # We can not override pre-defined value with subkey key.subkey := value
