Fix: close all file descriptors when executed as daemon

Both sessiond and consumerd support the option "-d" to run as daemon. In
some specific cases, e.g. when launched from dpkg installation scripts,
file descriptors 3, 4, 5 are left open and don't seem to have O_CLOEXEC
flag set, so the install script hangs because the sessiond still holds a
reference to them. daemon(3) only closes standard FD 0, 1, 2.

Fix this issue by closing all file descriptors after calling daemon(3).
Note: we make sure no file descriptor is opened before calling daemon(3)
by moving the init_thread_quit_pipe() call after the FD close.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>