Relocate some timestamp related tests from test_utils.py to
test_timestamp.py. The tested functions were relocated to timestamp.py
in the Related-Change.
Related-Change:I5b7ab3b2c150ec1513b3e6ebc4b27808d5df042c
Change-Id: I87f8f4e62b108f9e50510509ffd0ea3b3fb03177
Signed-off-by: Alistair Coles <alistairncoles@gmail.com>