daemon: Rename daemon.c as daemon-unix.c

An upcoming commit re-introduces daemon.c to have
common functions across daemon-unix.c and daemon-windows.c

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
daemon: Close standard file descriptors after detach for windows.

In the unit tests, we check for some logs stored in stderr. In case
of windows, unit tests fail because the child writes additional information
into stderr because it does not have it closed. This commit
closes standard file descriptors for windows too.

Because the functions related to closing file descriptors is common
for both windows and unix, add it to the common daemonization file
daemon.c

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
daemon: Move some common code to daemon.c

We have some common code between daemon-unix.c and
daemon-windows.c. Move them to daemon.c

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>