Refactored bosherr to match bosh-agent changes

- bosherr.Error & Errorf are now automatically validated by go vet

[#83520428]

Signed-off-by: Christian Williams <cwilliams@pivotal.io>
Add error.WrapErrorf to `go vet` checks.

[#83520428]

Signed-off-by: Christian Williams <cwilliams@pivotal.io>