Storage service needs to get local dc:rack pair in some places and it
calls system keyspace's local_dc_rack() method for it. However, the
method returns back the data from sys.ks. cache which, in turn, was
previously initialized from snitch's data. This patch makes storage
service get location from snitch directly, without messing with system
keyspace.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>