Fix releasetools timeouts

Release tools test uses sleep(5) to make sure mtime on files change in a
visible way. Use hardcoded mtime instead of sleeps.

Improvement: 145.6s -> 65s

Test: atest releasetools_test
Bug: 277782284
Fixes: 277782284

Change-Id: I4d7b04707f3b6c5843cde883f43e95a1e7a69879