Time key in json logging with Fluentd

[jykae]

Issue

"time" field is reserved key in fluentd, https://github.com/fluent/fluentd/issues/3269 This seems to come from werelogs as cloudserver uses it for logging: https://github.com/scality/werelogs/blob/8c483f34ed034719d995b3c26d2013b96b50ad62/lib/Logger.js#L67

Proposal

Change "time" key name in json logging to work together with fluentd.