Updated CHANGELOG.md for release 1.51.1
Updated CHANGELOG.md for release 1.51.1

jonvestal/open-kilda,telstra/open-kilda,telstra/open-kilda,telstra/open-kilda,telstra/open-kilda,telstra/open-kilda,jonvestal/open-kilda,telstra/open-kilda,telstra/open-kilda,jonvestal/open-kilda,jonvestal/open-kilda,jonvestal/open-kilda