Change ballon integration test.
Change ballon integration test.

- Split test_rss_memory_lower() test so it can be called
from other tests

Signed-off-by: Andrei Sandu <dbc21552912e46b041d86cfb2348c8cc4a9bf089@amazon.com>

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