$IPS only expands to the first ip address in the array:

justin@box:~$ declare -a IPS=(10.10.1.3 10.10.1.4 10.10.1.5)
justin@box:~$ echo $IPS
10.10.1.3
justin@box:~$ echo ${IPS[@]}
10.10.1.3 10.10.1.4 10.10.1.5

Also adds calico-rr group if there are standalone etcd nodes.
Now if there are 50 or more nodes, 3 etcd nodes will be standalone.
If there are 200 or more nodes, 2 kube-masters will be standalone.
If thresholds are exceeded, kube-node group cannot add nodes that
belong to etcd or kube-master groups (according to above statements).

Fix mismatching inventory examples.
Add command examples.
Clarify groups use cases.

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>

Includes tox support for running unit tests.
Small note added to getting-started guide for using
inventory_builder.py

Also adds manual-only unit test.