(bug 58943) Archivebot: create unit tests for Timestripper

Unit tests for Timestripper.
(after removal of Month() class)

Change-Id: I875116dc68d5247da762c7d064dce978217ece9c
See-also-Change-Id: I58cbf7130434245d018fedc173cb1b0da3401d78
Merge "(bug 58943) Archivebot: create unit tests for Timestripper"