Allow setting IPblock status

[zeromind]

Currently, it's only possible to set "Static" (via various allocate options, get ip etc), or set the status to "Available" by freeing the IP.

Status "Reserved" only gets set when adding a subnet to a pool, which currently reserves

• Network address
• Broadcast address
• .0 and .255 in networks larger than /24

https://github.com/1and1/dim/blob/master/dim/dim/rpc.py#L1179-L1183

Having it not reserve those IPs is currently broken, see #220

As there's an API endpoint that allows to "free" "Reserved" IPs via a specific flag, it's a good idea to allow setting at least "Reserved". Most trivial use-case would be reserving an IP again that was freed by mistake.