Auto merge of #200 - edunham:remove-old-logs, r=larsbergstrom
Auto merge of #200 - edunham:remove-old-logs, r=larsbergstrom

Remove 5-day-old zipped logs from buildslave dirs every night

Low disk space command from https://github.com/servo/servo/wiki/Buildbot-administration#handling-low-disk-space . We should no longer need to escape the semicolon, since Bash eats semicolons but Salt doesn't (right?)

Salt cron syntax from https://docs.saltstack.com/en/latest/ref/states/all/salt.states.cron.html

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rwaweber/saltfs,UK992/saltfs,UK992/saltfs,ALikhachev/saltfs,servo/saltfs,ALikhachev/saltfs,setupminimal/saltfs,setupminimal/saltfs,rwaweber/saltfs,servo/saltfs,setupminimal/saltfs,UK992/saltfs,ALikhachev/saltfs,rwaweber/saltfs