Fix incorrect exception raised during evacuate

This change creates a new exception 'ComputeServiceInUse'
to better represent the error when trying to evacuate
an instance with a running compute service. Also, it adds
a missing test for evacuate API v3.

Closes-Bug: #1230282

Change-Id: I1c4edb01e84cd2a89879bca9c99f5e38f47e16fb
Merge "Fix incorrect exception raised during evacuate"