Fix wrong key for 'usage.summary.instances' in CSV summary

In the project overview, the key for 'usage.summary.instances' the CSV
summary is wrong, it should be "Active Instances" instead of "Total
Active VCPUs".

Change-Id: Idf09fee592d522b7ebf5cffd0ce31240407c59d0
Closes-bug: 1288020
Merge "Fix wrong key for 'usage.summary.instances' in CSV summary"