Control periodic reboot on the bots and disable it by default

[GoogleCodeExporter]

The server currently tries to reboot all bots on an schedule. It's very heavy 
handed. It's a nice feature but should default to 'off'!

Options to control this behavior:
- Set state['periodic_reboot'] = <cycle in seconds> via bot_config to enable 
this.
Then the state can be enabled as desired on the relevant bots in bot_config.py.

- Completely control periodic reboot locally, e.g. remove the server-side logic 
for this.
We lose the ability to fuzz the duty cycle but we gain the removal of a fair 
amount of server-side code, which a much simpler client side implementation. 
Given that this periodic reboot is not desired to reboot completely broken 
bots, we do not lose functionality. Most of the implementation can be done in 
either bot.py or os_utilities.py with minimal support from bot_main.py.

- Add a BotSettings.periodic_reboot.
Bad idea, just stated here for completeness.

Original issue reported on code.google.com by maruel@chromium.org on 28 Nov 2014 at 2:36

• Blocked on: #184

[GoogleCodeExporter]

One reason I prefer #2 to #1 is that I do not want to add further "magic" state 
value. There's already dimensions['id'] that is magic and I'd prefer to limit 
this as much as possible.

Original comment by maruel@chromium.org on 28 Nov 2014 at 2:38

[GoogleCodeExporter]

Original comment by maruel@chromium.org on 1 Dec 2014 at 3:46

• Now blocked on: #184

[GoogleCodeExporter]

Original comment by maruel@chromium.org on 3 Dec 2014 at 6:21

• Changed state: Fixed