Make db API respect context show_deleted

Currently the soft-delete aware stuff in the DB api only respects
flags passed in directly, not the context.show_deleted, so align
the code with what is implied by existing comments and respect
the flag in the context too.

Change-Id: I88cd1a8862a2a53c314849e11d026182180bce9b
blueprint: request-scoping-policy
Merge "Make db API respect context show_deleted"