Make kubectl run attach behave like docker run

Have stdin closed by default, can be left open with --leave-stdin-open.
Add e2e tests for the behavior.

contrib/completions/bash/kubectl

@@ -753,6 +753,7 @@ _kubectl_run()
     flags+=("--image=")
     flags+=("--labels=")
     two_word_flags+=("-l")
+    flags+=("--leave-stdin-open")
     flags+=("--limits=")
     flags+=("--no-headers")
     flags+=("--output=")