Clean-up in BridgeOperationalState

The main fix is moving null-checks on iid before their first use.

db and changes are only used in the constructor, they don't need to
be in the instance; since the class isn't serializable removing the
fields doesn't change anything external.

Java 7 improvements: <> operator and merged exceptions.

Use Optional.fromNullable() to simplify some Optional creation code
and avoid double calls to getAugmentation().

Change-Id: Id6b8a13c46d2b38b23f215f200314151b9eb2b0a
Signed-off-by: Stephen Kitt <skitt@redhat.com>