1.7 Release Branch Cut

Hi team,

Yesterday (July 21) we cut the release branch for the upcoming 1.7 release.

From now on, any changes that should to go into the 1.7 release will need to be cherry-picked from master to the release-1.7 branch.

Please see https://github.com/istio/istio/wiki/Istio-Release-1.7 for all details about the 1.7 release, including information about how to cherry-pick changes.

Jonh Wendell, on behalf of the Release Managers team for 1.7.