tests: Handle test retries through the same queue

tests: Handle test retries through the same queue

This removes the separate rerun step from the parallel-vm.py processing
and instead, simply requeues the failed test cases into the same queue
that is used for the initial run. This is simpler and more efficient
since reruns start as soon as any VM is ready for processing them
instead of having to wait for all VMs to complete the first round.
Furthermore, this allows VMs to be stopped sooner when no more test
cases remain and that is helpful especially with the time travel patches
that make the wait-for-next-test step in the VM use all available CPU.

Signed-off-by: Jouni Malinen <j@w1.fi>