Bug 960 : Avoid adding redundant Openflow Controller entries

* Added IT for reproducing the problem;
* Enhanced ConfigurationService.setOFController() to detect duplicate
  targets and update rows instead of adding new ones.

Log: https://gist.github.com/anonymous/4ce9b2abdecda3c5e7fa

Change-Id: Ifedc351e849a18feb66b6025189495cb991c38f2
Signed-off-by: Flavio Fernandes <ffernand@redhat.com>