igt@kms_busy@.*hang.* are agonizingly slow on all platforms
These tests are responsible for a significant amount of the overall reported time of a CI FULL run:
- shard-skl: 1.7% (~4 minutes)
- shard-kbl: 2.8% (~3.5 minutes)
- shard-apl: 2.2% (~4 minutes)
- shard-glk: 1.8% (~4 minutes)
- shard-icl: 1.9% (~4 minutes)
- shard-tgl: 2.8% (~5.5 minutes)