_getAvailableProcessManagers() {
        const available = {};

        this._extensions.forEach((ext) => {
            each(ext.processManagers, (pm, name) => {
                if (!fs.existsSync(pm)) {
                    return;
                }

                available[name] = pm;
            });
        });

        return available;
    }
Gets a list of the available process managers from all of the extensions

@return {Object} hash of all process managers indexed by name
@method _getAvailableProcessManagers
@private