Fix FindBugs warnings in blueprint and enable enforcement

Warnings fixed:
- OpendaylightNamespaceHandler(line 83): "Usage of GetResource may be unsafe
  if class is extended". Made the class final so it can't be extended.

- BlueprintContainerRestartServiceImpl(line 140): "return value of this method
  should be checked". Log warning if 'await' returns false.

Change-Id: I1473acabd0a4126f5e5d2745292fcbff9a308462
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>