Bug 856594: Update buildbot master's buildbot.tac to keep more logs. r=nthomas

--HG--
extra : rebase_source : a27fffca6306b0363c9c73350401c34354d9f6f2
Bug 891880: differentiate talos per OS X revision; r=coop
Bug 894512 - Add panda-nomozpool slave class. r=aki
for "Split mozpool managed panda jobs away from non mozpool jobs"
Bug 894201: add clocksource=pit on linux+vmware; r=rail
Bug 889058: only use firewall on linux; r=Callek
Bug 882869: update Python build script to work on Lion and Mtn Lion; r=Callek