rcstream: add lvs, modify mountpoint

Adding stream.wikimedia.org as a low-traffic service, move rcstream to
the /rc location so that we can potentially add other services in the future.

Change-Id: I9bfc11844dfe88c6cf6f01bea12714da1c0853ad
Signed-off-by: Giuseppe Lavagetto <glavagetto@wikimedia.org>