set lowercase os[:family] for OpenBSD
set lowercase os[:family] for OpenBSD

this is consistent with other os'es and adheres to the principle of least astonishment

serverspec/specinfra,sorah/specinfra,hfm/specinfra,glenux/contrib-specinfra,uroesch/specinfra,r7kamura/specinfra,chinthakagodawita/specinfra,lurdan/specinfra,verisign/specinfra,hideyuki/specinfra,stefanhorning/specinfra,mizzy/specinfra,aibou/specinfra,minimum2scp/specinfra,sergueik/specinfra,elibus/specinfra,mactkg/specinfra,k0kubun/specinfra,higanworks/specinfra,miketheman/specinfra,chef-partners/specinfra-cisco,sean-horn/specinfra,edolnx/specinfra,ihassin/specinfra,nurse/specinfra,pfaffle/specinfra,thenexus6/specinfra,chorrell/specinfra,skamithi/specinfra,bodgit/specinfra,seroron/specinfra,electrical/specinfra,stoned/specinfra,RoboticCheese/specinfra,winebarrel/specinfra,gh2k/specinfra,optimizely/specinfra,tacahilo/specinfra