Update comments for keystone precision and fernet

Keystone is moving to drop microsecond precision across the board
for consistency. This updates the comments to reflect that the sleep
is not a bug and expected.

Change-Id: I8beaeb4a94f0de1ad5d89df9ec77a1ae1b08a9d1
Closes-Bug: #1517697
Closes-Bug: #1513538
3 files changed