tests: Return when pytest is in discovery mode
tests: Return when pytest is in discovery mode

Signed-off-by: Gabriel Ionescu <11a253f1dc12bb9191751579b54ccff8c3511f57@amazon.com>

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