Swagger API: OS.json Change uptime and remove reboot

The uptime method should return the time from boot rather the time at
boot.

The reboot will not be supported at this phase

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Http Server: Add stub for shutdown

The shutdown function is called from the os api,
because it is part of the osv it need to be stub so the standalone
server would link.

Its stub implementation will not interfere with the linux operating
system.

Calling shutdown will exit the server

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Http Server: Implement the os api

The swagger os.json api defines a set of os related operations.
The self explenatory list that will be supported is:

The following would work with GET:
http://192.168.122.89:8000/os/manufacturer
http://192.168.122.89:8000/os/uptime
http://192.168.122.89:8000/os/date
http://192.168.122.89:8000/os/memory/total
http://192.168.122.89:8000/os/memory/free

The following would work with POST
http://192.168.122.89:8000/os/shutdown

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Http Server: Show code generation during build

Make code generation visible during build so it's obvious that some of
the source files are generated.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>