4499: Normalize manifest in one_task_per_input_file

* arvados.job_setup.one_task_per_input_file now calls cr.normalize()
  before creating tasks.

* Added unit test in test_sdk.py to confirm that the expected number of
  tasks are created when called on a normalized manifest.
Merge branch '4499-one-task-per-input-file-normalize'

Fixes #4499.