Added possibility to specify a default user for bulk_create_with_history

[bmampaey]

Description

Right now, if we want to specify a user when calling bulk_create_with_history, we have to set the user on _history_user for all objects. The proposed change would allow to simply specify a default user when _history_user is not set.

Related Issue

Add possibility to specify a default user for bulk_create_with_history #635

How Has This Been Tested?

I have added 2 tests:

• one for HistoryManager.bulk_history_create
• one for bulk_create_with_history

They both pass. 3 other tests, seemingly unrelated, don't pass, but they didn't pass in master either.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run the make format command to format my code
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.

[rossmechanic]

looks good! have been meaning to do this. need to fix some tests tho

[rossmechanic]

closing. Picked this up in #653