Consider probing each system for memory usage and report when above some threshold

[servilla]

A system in-use memory probe should be considered to alert admins of potential out-of-memory issues. This would be similar to the uptime and readonly probes in the soh/tree/master/src/soh/asserts/server.py module. For example, the following information may be used to ascertain memory use:

cat /proc/meminfo
MemTotal:        8128040 kB
MemFree:         2102636 kB
MemAvailable:    6776160 kB