Allow burnin with hidden OSes
Allow burnin with hidden OSes

burnin is a cluster/testing feature, so it makes sense that a hidden OS
can be used for it.

Signed-off-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>
Reviewed-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>

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