Add error_on_missing_backend_type option. If this is true and backend is nil, an error will be raised.
Add error_on_missing_backend_type option.
If this is true and backend is nil, an error will be raised.

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