Find out how to package runtimes.json into wskdeploy binary

As a quick fix in PR #1017, I have moved runtime `json` into `runtimes.go` but we want to bring back `runtimes.json` back to maintain portability of `wskdeploy` where for adding any new runtime, we can just update the `json` file. I found a way to bundle `json` into wskdeploy binary using `packr` but need to look into it more and see how we can make it part of binary.