ctdb-daemon: Fork when not interactive and test mode is enabled

ctdb-daemon: Fork when not interactive and test mode is enabled

There is no sane way of keeping stdin open when using the shell to
background ctdbd in local_daemons.sh.  Instead, have ctdbd fork when
not interactive and when test mode is enabled.  become_daemon() can't
be used for this: if it forks then it also closes stdin.

For the interactive case, become_daemon() wasn't doing anything
special, so do nothing instead.

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