Bug 2239: Fixed manager.neutron bugs detected by FindBugs.

  * OVSDBPluginEventHandler
    * getSwitchIdFromInterface(): Fixed possible null dereference.
    * The following fields should not be static because they are handled
      by instance methods only.
      * integrationBridgeName
      * failmode
      * protocols
      * portname
    * getSystemProperties() should close FileInputStream.
    * getInternalBridgeUUID(): Map.entrySet() should be used rather than
      Map.keySet().
    * Eliminate trailing/succeeding whitespaces in log message.
  * PortHandler
    * canModifyInterface(): Boolean instances need to be compared using
      equals(Object).

Change-Id: Ia9b83547ffe4efe80b328925cddd1ecf71865ba5
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>
(cherry picked from commit 3c4be2c0675464708eece7433c4d5016c1c28aac)
Merge "Bug 2239: Fixed manager.neutron bugs detected by FindBugs." into stable/helium