QA: Acquire instance via method
QA: Acquire instance via method

Also make “used” a property.

Signed-off-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>
Reviewed-by: Bernardo Dal Seno <dcdd79c5479cb9d1329ec01d126f02cb045aa103@google.com>

yiannist/ganeti,grnet/snf-ganeti,leshchevds/ganeti,onponomarev/ganeti,ganeti/ganeti,ganeti-github-testing/ganeti-test-1,andir/ganeti,apyrgio/ganeti,apyrgio/ganeti,bitemyapp/ganeti,andir/ganeti,apyrgio/snf-ganeti,yiannist/ganeti,yiannist/ganeti,onponomarev/ganeti,dimara/ganeti,ganeti-github-testing/ganeti-test-1,dimara/ganeti,mbakke/ganeti,mbakke/ganeti,andir/ganeti,leshchevds/ganeti,apyrgio/snf-ganeti,leshchevds/ganeti,bitemyapp/ganeti,ganeti/ganeti,grnet/snf-ganeti,ganeti/ganeti,mbakke/ganeti