Provide explicit task create and update value in controller tests

Assign an explicit created_at and updated_at datetime value to task DB
fixtures, it be used to fixes race condition in TasksController test
cases.

Closes-Bug: #1274365

Change-Id: I9f13c7e0e97085faac15713342808722a6692178
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Merge "Provide explicit task create and update value in controller tests"