Anil noticed there was a race condition here where we might write

Anil noticed there was a race condition here where we might write
an ovsdb-node to the operatational store before recording the
TransactInvoker we needed for people to be able to use it to write to
ovsdb.  This fixes that by imposing the order:

1)  Record the TransactInvoke for the ovsdb-node (internally)
2)  Write the ovsdb-node to OPER
3)  Register callbacks for monitors from ovsdb

Change-Id: I55202678521065b1a8c2f018a9f229b6be263a48
Signed-off-by: Ed Warnicke <hagbard@gmail.com>