tools/bootconfig: Add testcases for repeated key with brace

Add a testcase for repeated key with brace parsing issue.

Link: https://lkml.kernel.org/r/160068150176.1088739.409481347784771987.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>