testing: memory monitor thread
testing: memory monitor thread

Each test spawns a new thread which computes Firecracker's memory
overhead by summing up the vss values reported by pmap, excluding the
guest's memory region. This should be identified by starting address
(logged when the guest starts), but until log flushing issues are
solved, it's identified by total size, known from the machine-config api
call.

Signed-off-by: Alexandra Iordache <750ec4522de000f31ad44d64614ad5747f238032@amazon.com>

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