Pass IP addresses directly to Reaper

[SolomonShorser-OICR]

It would be convenient to be able to pass an IP address directly to the Reaper when you only want to reap one VM, rather than having to edit the kill-list.json file. For example:

Reaper --ip 111.222.33.4

Or a list of IPs:

Reaper --ip 111.222.33.4 111.222.33.5 111.222.33.6

[denis-yuen]

Sounds good.

As a temporary workaround, there's also echo "[\"111.222.33.4\",\"111.222.33.5\"]" > test.json ; Reaper -- ip test.json