[LOOM] Some nsk/jdi tests fail due to needing too many virtual threads

These 2 tests try to create 10 vthreads and have them all block on a synchronized method call, but on some hosts there are not enough carrier threads to support pinning all 10 vthreads (by default there is 1 per core), so the test deadlocks. -Djdk.defaultScheduler.parallelism=<n> could be used with the debugee to ensure there are enough carrier threads.

vmTestbase/nsk/jdi/EventRequestManager/stepRequests/stepreq002/TestDescription.java
vmTestbase/nsk/jdi/EventRequestManager/deleteEventRequests/delevtreqs002/TestDescription.java

Not this is basically the same issue as we see with JDK-8282383, but those tests fail when there are even fewer cores.