dhcp: adjusted addrconf lease details

- Renamed dhcp4.serveraddress to server_id and fixed
  to not mix it with the boot-server-address (siaddr)
- Renamed dhcp4.servername to boot-server-name
- Added relay-address (giaddr) to the dhcp4 lease
- Use an opaque type for dhcp4 client-id
- Request posix timezone and dhcp6 boot-url settings
- Adjusted options in lease file and leaseinfo dump
- Adjusted objectmodel transfer and leasefile data
leaseinfo: consistently use prefixlen in ROUTES

Today the netmask is never used to set up something.
Consistently use prefixlen for ipv4 and ipv4 routes
so there is no need to relalculate for iproute2.
Merge pull request #157 from mtomaschewski/dhcp-leases