Corrected non-existent process dump file handling on resurrect.

This patch fixes the handling of a non-existent process dump file (`~/.pm2/dump.pm2`). The try.. catch block was not catching the error from `fs.readFileSync` (nor should fs.readFileSync be used anymore [per Node API docs](http://nodejs.org/api/fs.html#fs_fs_exists_path_callback)), and so the process exited ungracefully with an error when the dump file wasn't there. Also, `process.exit` was undefined, so I used `exitCli` instead (as in other CLI methods).