Feature: configure ip_version

[pdesgarets]

Fixes https://github.com/ggiamarchi/vagrant-openstack-provider/issues/302 Adds ip_version option (4 or 6) to define what IP should be used to ssh into the instance.

Possible important change : it does not use the first network defined in the config at all costs, but checks every network from the config to see if one contains an IP of the desired version, even if it is not the first ranked.

~Some "real use" tests should be performed before merging.~ Done, seems to work fine

I added some unit tests, they might not cover every possible scenario.

[coveralls]

Coverage decreased (-0.06%) to 87.677% when pulling 73d7bb220ded11f2c82b96a9b9b9580cc68612be on illuin-tech:feat/master/ip_version into 4ee2d594e9d98968c9ea44c0cdc7e864eff5f45b on ggiamarchi:master.

[pdesgarets]

Renamed to WIP To-do :

• [x] use version returned by the API instead of guessing it