Fix so that operational store correctly removes bridge-external-ids

Fix so that operational store correctly removes bridge-external-ids

Before, if a bridge-external-ids entry was removed on ovsdb, we didn't
remove it from the operational store.

This is an artifact of using *merge* rather than *put*.
Using merge is *still* a good idea for us, but what was happening
was basically this.

Say we got a report in the operational store of

[bridge-external-ids1, bridge-external-ids2]

which we dutifully merged.

Then we got a report of
[bridge-external-ids2]

when that is *merged*... the protocol1 entry is left dangling,
because its a *merge*.  To compensate, we have to be *very*
specific about wanting to remove bridge-external-ids1.

Change-Id: I7bb7e3264176604f3a01f90231cae99026148f2f
Signed-off-by: Ed Warnicke <eaw@cisco.com>