Fix Mercurial version format strings in unittest

In hgtests.py we let hg create the timestamp in UTC but create the
reference timestamp in the local timezone. Since GIT is giving us the
localtime in the test by default lets do the same thing for Mercurial.

Signed-off-by: Jan Blunck <jblunck@infradead.org>
Extend fixture to create commits with a specific timestamp

This is the required preparation of the framework for the tests that check
tar_scm for always creating a binary identical tarball from the same commit.

Signed-off-by: Jan Blunck <jblunck@infradead.org>
Use commit timestamp as mtime for files in tarball

Otherwise the tarball will not be binary identical even if it is created
from the same source tag. In some cases this will lead to unnecessary
rebuilds.

Signed-off-by: Jan Blunck <jblunck@infradead.org>