fileReady is not idempotent

[mhrivnak]

Bug Report

What did you do?
call Set() twice in a row, or Unset() twice in a row. If an operator is going to intelligently change the value of its readiness probe during runtime, there is a chance that multiple events will result in the value being set or unset.

For example, consider a case where an operator starts and begins an upgrade workflow. It sets not-ready as requested by OLM. If something goes wrong and the operator exits with an error, the last thing that will happen in main.go (based on a defer statement) will be to call Unset(). That will result in an error, because the file will be not-found.

What did you expect to see?
No error returned.

What did you see instead? Under which circumstances?
Error returned

Environment

• operator-sdk version:
  0.9.0

Possible Solution

If Set() finds that the file already exists, return nil.

If Unset() fails to unlink the file because it doesn't exist, return nil.

[jmrodri]

Assigned to myself to track the PR that @djzager has done.