libfaketime: fix problem with TIMESTAMP_FILE synchronization

Clearing and writing to TIMESTAMP_FILE is not atomic and libfaketime
can read empty file which represents default behavior and returning
realtime. Create and move new file is atomic and prevent this issue.
7 jobs for libfaketime-fix-file-sync in 1 minute and 16 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #54392
docker linux amd64
test:comparative:kresd

00:00:52

passed #54393
docker linux amd64
test:latest:kresd

00:01:15

passed #54389
docker linux amd64
test:pep8

00:00:26

passed #54390
docker linux amd64
test:pylint

00:00:53

passed #54395
docker linux amd64
test:sanity:pdnsrecursor

00:00:34

passed #54394
docker linux amd64
test:sanity:unbound

00:00:36

passed #54391
docker linux amd64
test:unittests

00:00:34