Account for /dev/shm in memory usage

[holzman]

Problem

/dev/shm usage is not accounted for in the resource usage. (We're only just increasing this space over the k8s default, so we didn't notice up until now).

Proposed Solution

Add psutil.virtual_memory().shared to the RSS metric (probably should a new rss_plus_shm metric and display that instead, to be accurate..)

If this idea LGTY I can send a PR.