Use double quote to allow spaces in filename [backport]

Compared to single quote, which is not a valid character on Windows
platform for commandline, double quote works for all the platforms.

Change-Id: I46c38d208b9b61aed4b82f8ac444a76b2360d171
Reviewed-on: http://review.couchbase.org/7041
Reviewed-by: Dustin Sallings <dustin@spy.net>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Reviewed-on: http://review.couchbase.org/8388
Reviewed-by: Steve Yen <steve.yen@gmail.com>
Tested-by: Steve Yen <steve.yen@gmail.com>

src/couchdb/couch_os_process.erl

@@ -107,7 +107,7 @@ init([Command, Options, PortOptions]) ->
     process_flag(trap_exit, true),
     PrivDir = couch_util:priv_dir(),
     Spawnkiller = filename:join(PrivDir, "couchspawnkillable"),
-    CompleteCmd = "'" ++ Spawnkiller ++ "' " ++ Command,
+    CompleteCmd = "\"" ++ Spawnkiller ++ "\" " ++ Command,
     BaseProc = #os_proc{
         command=Command,
         port=open_port({spawn, CompleteCmd}, PortOptions),