Support error wrapping for locked state errors

[alec-rabold]

First off thank you for maintaining this project! It's such a great tool for automating TF workflows in code.

Feature

One addition that I believe would be helpful is a first-class error when there's an issue acquiring a state lock, as well as the LockInfo so that a force-unlock is possible if appropriate. The driving use-case for us is when the Terraform process unexpectedly exits early, requiring either manual intervention or a separate stderr logger to catch this.

I've created a pull request (#221) and was hoping to get some thoughts from you all.

Thanks!

[radeksimko]

#221 was just merged