ovsdb: bond_active_salve column's value should be durable when database restarts

According to RFC 7047, 'ephemeral' annotation does not guarantee
the values to be durable. This fix Removes this annotation.

VMware-BZ:  1332235

Signed-off-by: Andy Zhou <azhou@nicira.com>
Acked-by: Alex Wang <alexw@nicira.com>