Make more extensive use of the BaseUnitTestCase timestamp helpers.
Note: This patch makes progress towards uniform use of the base class,
but there are still more places to potentially inherit the base class.
Change-Id: I0cfe48182cafa83fb9edd439c9fbcfac37cdf1e6
Signed-off-by: Alistair Coles <alistairncoles@gmail.com>