Use memory_tracker service
Use memory_tracker service

The peakmem_tracker service has been deprecated in devstack and is
about to be removed, see [0]. Use the memory_tracker service instead.

[0] https://review.opendev.org/638409

Change-Id: I523b5f3734a7adc0001b58f9b14f79f15638b820

openstack-dev/grenade,openstack-dev/grenade