data_models.to_dict didn't convert values inside lists.
When serializing TLSContainer, the intermediates list that contains
bytes types wasn't converted properly.
to_dict now converts the items of a list recursively.
Add a test that checks if TLSContainer.to_dict is serializable.
Story 2009310
Task 43699
Change-Id: I3859c7fcefc89e91fdaecd139143e6a74d8b3c1b
(cherry picked from commit d25ed7aba6753285671e4f3b8c478c0e5e022e10)
db22c0b9da