mark containers.proxy params as stable on linux cells
mark containers.proxy params as stable on linux cells

[finishes #159909414](https://www.pivotaltracker.com/story/show/159909414)

cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release