Handle failed Read phase and updated Read script

[rucciva]

Since read script is also part of state, Read phase will always use the one stored and will ignore the updated one. So maybe when update is triggered and there is a change in read script, we should not execute update script and execute read script instead. If the new read produce change, then subsequent terraform apply need to be run to fully sync the state.

Also if read script fail after Create succeeded, terraform plan will fail, consider adding read_failed attribute and act on it when update. This changes will trigger Destroy->Create if update script is empty. User are left with two options: allow recreation, or manually do something so that read succeeded.