veyron/services/mgmt: implementing Revert() for the node manager

This CL:
- implements Revert() for the node manager
- simplifies the logic used for testing a new version of a node manager
- renames content.Content to content.Repository
- renames application.Shutdown to application.Stop
- renames exec.SetEnv and exec.GetEnv to exec.Setenv and exec.Getenv
	respectively

Change-Id: If58521eec37bc12c8f2de9ad89d1d571e9c51b33
12 files changed
tree: 586f009fd2824b443757fcb371e3196050a33c16
  1. examples/
  2. lib/
  3. runtimes/
  4. security/
  5. services/
  6. tools/