tools/bootconfig: Fix to use correct quotes for value

Fix bootconfig tool to select double or single quotes
correctly according to the value.

If a bootconfig value includes a double quote character,
we must use single-quotes to quote that value.

Link: http://lkml.kernel.org/r/159230245697.65555.12444299015852932304.stgit@devnote2



Cc: stable@vger.kernel.org
Fixes: 950313eb ("tools: bootconfig: Add bootconfig command")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>