daemon-windows: Implement --detach option for Windows.

daemon-windows: Implement --detach option for Windows.

When "--detach" is specified, a daemon will create a new
process with the same command line options as the parent.
Additionally, an undocumented command line option "--pipe-handle"
is passed to child. Once the child is ready to handle external
commands, it communicates with the parent that it is ready using
the pipe handle. The parent exits. This lets us run the daemons
in background. This will also help the unit tests because currently
most of the unit tests pass the '--detach' option to the daemons.

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