* p/ticket/10972:
[ticket/10972] Drop user deletion.
[ticket/10972] Tweak user addition.
[ticket/10972] Add destroy method to mock cache.
[ticket/10972] Add mock null cache.
[ticket/10972] Backport get_db from develop.
[ticket/10972] Added explicit checks for creating duplicate users.
[ticket/10972] Moved tests into appropriate places and added comments
[ticket/10972] Added methods for creating and deleting basic users