Add a metric to track "Wrong key returned" errors

[smukil]

This change adds "wrongKeyReturned" as a metric and increments it
everytime we see it in action.

This change was added as we noticed some of these error messages in
the logs, and we'd like to track the frequence of these errors.

Note that even prior to this change, we did not return the wrong key
back to the calling application but instead count it as a miss.

[arunagrawal84]

nit: Consider creating a method to log error, increment and print stack trace.

[smukil]

nit: Consider creating a method to log error, increment and print stack trace.

Thanks @arunagrawal84 . Added a new commit to do so.