system: deal with /var MFS more gracefully now that /var/log may need to carry large amounts of data

[fichtner]

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Is your feature request related to a problem? Please describe.

Since the removal of CLOG files log files can grow quite large and produce OOM for /var MFS consumers.

Describe the solution you like

Add a tmpfs upper limit to a separate /var/log MFS partition and/or narrow /var MFS to /var/log since the premise of the feature was to reduce logging write cycles and most of /var config use is moving to normal file system layout /usr/local instead.

Describe alternatives you considered

Removal of /var MFS? ;)

Additional context

IRC discussions also including OOM-protected syslog-ng process, which actually makes the issue worse for going OOM with that option enabled.