Adds class method to clear backend
Adds class method to clear backend

So that we can reset the backend between runs and avoid re-using a
connection when the host may have changed.

tacahilo/specinfra,gh2k/specinfra,verisign/specinfra,ihassin/specinfra,sergueik/specinfra,minimum2scp/specinfra,stefanhorning/specinfra,hfm/specinfra,uroesch/specinfra,serverspec/specinfra,mizzy/specinfra