Test for unicode names in AccountBroker.merge_items()

ContainerBroker.merge_items() had a bug in it where non-ASCII Unicode
names would possibly result in duplicate entries in container
databases. AccountBroker.merge_items() doesn't do the same
bulk-operations tricks that ContainerBroker does, so it doesn't
currently have the bug. This commit just adds a test to ensure the bug
doesn't creep in should someone decide to make AccountBroker look more
like ContainerBroker someday.

Change-Id: Id2ac129828dbdf55b609d839ce4d9d42437ee0a3
Merge "Test for unicode names in AccountBroker.merge_items()"