tools/bootconfig: Add testcase for tailing space

Add testcases for removing/keeping tailing space
in the value.

Link: https://lkml.kernel.org/r/160068151151.1088739.3469541807296024227.stgit@devnote2

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