Add reset cli flag

This is an initial stab at the first of [four changes](https://github.com/eslint/eslint/issues/692#issuecomment-38209348) discussed in #692. It adds a `--reset` (`-r`) flag to the cli options that resets all default rules to be off. As @nzakas suggested, it simply doesn't load `conf/eslint.json`.

@visionmedia [proposed](https://github.com/eslint/eslint/issues/692#issuecomment-38236247) only turning off the stylistic rules and leaving syntax errors and the "Possible Errors" rules enabled. This change does not do that but instead turns everything off. If there is consensus that the proposed behavior is desirable, I can go ahead and implement that.