Remove owner_is_tenant from RequestContext

This appears to be a leftover from glance, and we don't support
anything other than tenant-scoped requests.

Change-Id: Ibce0e38ee24f18de24733a35d25c90c03b46dc6e
blueprint: request-scoping-policy
Fix show_deleted errors in RequestContext

get_admin_context takes a read_deleted argument which is ignored,
and we don't include the read_deleted value in to_dict output.
Fixing this means we can respect this flag in the DB API, which
currently we do not.

Change-Id: Id0906983b93cd2526580942390f7992fb2cb5504
blueprint: request-scoping-policy
Merge "Remove owner_is_tenant from RequestContext"
Merge "Fix show_deleted errors in RequestContext"