CLI: Prevent incompatible options to be selected
CLI: Prevent incompatible options to be selected

This patch makes CLI abort if more than one backend is selected.

dimara/ganeti,leshchevds/ganeti,apyrgio/snf-ganeti,yiannist/ganeti,leshchevds/ganeti,andir/ganeti,ganeti/ganeti,leshchevds/ganeti,mbakke/ganeti,mbakke/ganeti,yiannist/ganeti,dimara/ganeti,bitemyapp/ganeti,apyrgio/ganeti,andir/ganeti,yiannist/ganeti,onponomarev/ganeti,grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,bitemyapp/ganeti,andir/ganeti,apyrgio/ganeti,ganeti/ganeti,ganeti/ganeti,onponomarev/ganeti,mbakke/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/snf-ganeti