tests.cluster: Add test for VerifyConfig
tests.cluster: Add test for VerifyConfig

Check if VerifyConfig complains about orphan disks.

Signed-off-by: Alex Pyrgiotis <6383a799dda2258eec8fa26a3ce2ec8a7d552341@grnet.gr>
Signed-off-by: Aaron Karper <99cc1031546340b2b8ced5fe338b5890677a56ca@google.com>
Reviewed-by: Aaron Karper <99cc1031546340b2b8ced5fe338b5890677a56ca@google.com>

bitemyapp/ganeti,bitemyapp/ganeti,leshchevds/ganeti,apyrgio/ganeti,ganeti/ganeti,ganeti/ganeti,grnet/snf-ganeti,dimara/ganeti,leshchevds/ganeti,ganeti/ganeti,grnet/snf-ganeti,onponomarev/ganeti,andir/ganeti,andir/ganeti,yiannist/ganeti,mbakke/ganeti,apyrgio/ganeti,andir/ganeti,mbakke/ganeti,dimara/ganeti,onponomarev/ganeti,mbakke/ganeti,yiannist/ganeti,yiannist/ganeti,leshchevds/ganeti