Add missing tests for nova.db.api.instance_system_metadata_*

blueprint db-api-tests

Change-Id: I2a7b24d3b7b0fa7af004a8106dfef29178a9aaa3
Drop unused _virtual_power_settings global.

We aren't making use of this global so drop it.

Change-Id: I66cdeb4a42af6785cb49c0768e6ba0f1bc98625c
Merge "Add missing tests for nova.db.api.instance_system_metadata_*"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp