build: Move the default CTDB socket from /tmp to /var/run/ctdb

build: Move the default CTDB socket from /tmp to /var/run/ctdb

Use /var/run/ctdb/ctdbd.socket because there might be other daemons
that need sockets in the future.

The local daemons test code to create a link for the default
convenience socket has to be removed because the link can't be created
as a regular user in the new location.  This should be OK since all
calls to the ctdb tool in the test code should be wrapped in onnode.
When debugging tests, a developer will have to set CTDB_SOCKET by
hand.

Signed-off-by: Amitay Isaacs <amitay@gmail.com>
Pair-programmed-with: Martin Schwenke <martin@meltin.net>

(This used to be ctdb commit dc67a4e24af9d07aead2a1710eeaf5d6cc409201)