Log original error when attaching volume fails

We have a race in the gate to attach an encrypted volume and the only
thing we see in the logs is the DeviceIsBusy error which makes this hard
to debug.

This change logs the original error so we can dig deeper into the root
cause.

Related-Bug: #1348204

Change-Id: I7d0f2571e80a4e55133f823d2a04feaf4dddf2e5
Merge "Log original error when attaching volume fails"