tests: refactor batch assignment mechanism
tests: refactor batch assignment mechanism

Simplified the mechanism for finding the matching batch
inside the scheduler for each of the tests.
The mechanism (i.e next) stops the iteration when the
matching batch is found based on some given regex search.

Signed-off-by: keyangxie <ecd7bd01534c8674520527b4a78fc5e108454b6f@gmail.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker