workflow - update workflow object. meta - Any additional information to pass to the backend which is not workflow properties callback - f(err, workflow)
function updateWorkflow(workflow, meta, callback) {
            if (typeof (meta) === 'function') {
                callback = meta;
                meta = {};
            }

            if (workflows[workflow.uuid]) {
                if (_wfNames().indexOf(workflow.name) !== -1 &&
                    workflows[workflow.uuid].name !== workflow.name) {
                    return callback(new e.BackendInvalidArgumentError(
                      'Workflow.name must be unique. A workflow with name "' +
                      workflow.name + '" already exists'));
                } else {
                    workflows[workflow.uuid] = clone(workflow);
                    return callback(null, workflow);
                }
            } else {
                return callback(new e.BackendResourceNotFoundError(
                  'Workflow does not exist. Cannot Update.'));
            }
        }