tools/bootconfig: Add testcase for show-command and quotes test

Add testcases for the return value of the command to show
bootconfig in initrd, and double/single quotes selecting.

Link: http://lkml.kernel.org/r/159230247428.65555.2109472942519215104.stgit@devnote2



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