When updategraph service is enabled, a special value 'default'
from DHCP response will now initialize the system with an empty
configuration instead of existing minigraph.
A DHCP response without option 224 will remain the current behavior
of skipping graph update and use existing default minigraph.
- Add a functionality to get SNMP community from DHCP (option 224)
- Add a functionality to get minigraph from http service instead of using default minigraph
- The url for graph service is passed through DHCP option 225
- This feature is by default disabled. Modify rule/config to enable it on build time, or modify /etc/sonic/graph_service_url on run time.
- Fix a bug that getting hostname from DHCP is not working correctly
