Remove container env var from libcontainer

Update tests to use native driver
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

integration/container_test.go

@@ -1044,7 +1044,6 @@ func TestEnv(t *testing.T) {
 	goodEnv := []string{
 		"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
 		"HOME=/",
-		"container=docker",
 		"HOSTNAME=" + utils.TruncateID(container.ID),
 		"FALSE=true",
 		"TRUE=false",

integration/utils_test.go

@@ -190,6 +190,7 @@ func newTestEngine(t utils.Fataler, autorestart bool, root string) *engine.Engin
 	job := eng.Job("initserver")
 	job.Setenv("Root", root)
 	job.SetenvBool("AutoRestart", autorestart)
+	job.Setenv("ExecDriver", "native")
 	// TestGetEnabledCors and TestOptionsRoute require EnableCors=true
 	job.SetenvBool("EnableCors", true)
 	if err := job.Run(); err != nil {