Add timestamp filtering cases in storage tests

Fixes bug #1224305

The group by statistics storage tests don't have any test cases for
timestamp filtering.

The group by statistics API tests already have test cases for
timestamp filtering with the same test database, so these test cases
are simply copied over to the storage tests.

The added test cases are group by

a) single field with start timestamp after all samples
b) single field with end timestamp before all samples
c) single field with start timestamp
d) single field with end timestamp
e) single field with start and end timestamps
f) single field with start and end timestamps and query filter
g) single field with start and end timestamps and period
h) single field with start and end timestamps, query filter, and period

Change-Id: I2896e6bcdca5a87b9ce4262599e77832274943b4
Merge "Add timestamp filtering cases in storage tests"