fixed: when start with a js inside dir, no check on the dirs in var

e.g.,

[root@ctbd-demo cthadoop]# nin start myct-httpd
[INFO] nin.json of /opt/cthadoop/node_modules/myct-httpd read.
[INFO] entering dir: /opt/cthadoop/node_modules/myct-httpd.
[INFO] start (0) action: {"type":"forever","content":"lib/main.js"}.

fs.js:427
  return binding.open(pathModule._makeLong(path), stringToFlags(flags), mode);
                 ^
Error: ENOENT, no such file or directory '/opt/cthadoop/node_modules/myct-httpd/var/lib/main.js.log'
    at Object.fs.openSync (fs.js:427:18)
    at _fe_startDaemon (/usr/lib/node_modules/nin/lib/start.js:89:14)
    at Object.foreverStart [as forever] (/usr/lib/node_modules/nin/lib/start.js:117:3)
    at /usr/lib/node_modules/nin/lib/start.js:150:39
    at /usr/lib/node_modules/nin/node_modules/async/lib/async.js:610:21
    at /usr/lib/node_modules/nin/node_modules/async/lib/async.js:249:17
    at iterate (/usr/lib/node_modules/nin/node_modules/async/lib/async.js:149:13)
    at async.eachSeries (/usr/lib/node_modules/nin/node_modules/async/lib/async.js:165:9)
    at _asyncMap (/usr/lib/node_modules/nin/node_modules/async/lib/async.js:248:13)
    at Object.mapSeries (/usr/lib/node_modules/nin/node_modules/async/lib/async.js:231:23)