Add helper function for querying cluster properties
Add helper function for querying cluster properties

As more and more configuration values will have to be made available via
queries, this patch adds a small helper method for these.

Signed-off-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>
Reviewed-by: Helga Velroyen <2d0126b1ec6f9ec5cbec4a7012aa14faeaef10f5@google.com>

leshchevds/ganeti,ganeti/ganeti,yiannist/ganeti,mbakke/ganeti,ganeti/ganeti,leshchevds/ganeti,mbakke/ganeti,onponomarev/ganeti,andir/ganeti,yiannist/ganeti,onponomarev/ganeti,andir/ganeti,andir/ganeti,mbakke/ganeti,ganeti/ganeti,yiannist/ganeti,leshchevds/ganeti