Summary:
`GetCurrentTime()` is used to populate `creation_time` table property during flushes and compactions. It is safe to ignore `GetCurrentTime()` failures here but they should be logged.

(Note that `creation_time` property was introduced as part of TTL-based FIFO compaction in #2480.)

Tes Plan:
`make check`
Closes https://github.com/facebook/rocksdb/pull/3231

Differential Revision: D6501935

Pulled By: sagar0

fbshipit-source-id: 376adcf4ab801d3a43ec4453894b9a10909c8eb6