Clarify flakiness of WindowTracingPerfettoTest

Move busyWaitForDataSourceRegistration to non static set up,
otherwise the failure will be module error (break test count).

Dump perfetto status if the target data source is not found.

Bug: 372558379
Flag: EXEMPT TEST_ONLY
Test: atest WindowTracingPerfettoTest

Change-Id: Idb8fef6aaaff3102e6c5d4fad467530c52f3b5d2