Updated Openstack to terraform 0.12 (#5062)

* update openstack to terraform 0.12(.5)

* replace cluter.tf with cluster.tfvars

* update README.md to terraform 0.12

* update Openstack CI tests to use terraform 0.12

* specify terraform version in openstack README

* gitlab CI to copy cluster.tfvars in case of openstack provider

* The terraform/openstack dynamic inventory can read
tfstate v4 (generated by terraform 0.12) and convert them internally
ro v3 (as generated by terraform 0.11.x).

Additionally the script has been updated to Python 3.

contrib/terraform/openstack/sample-inventory/cluster.tfvars

@@ -0,0 +1,58 @@
+# your Kubernetes cluster name here
+cluster_name = "i-didnt-read-the-docs"
+
+# SSH key to use for access to nodes
+public_key_path = "~/.ssh/id_rsa.pub"
+
+# image to use for bastion, masters, standalone etcd instances, and nodes
+image = "<image name>"
+
+# user on the node (ex. core on Container Linux, ubuntu on Ubuntu, etc.)
+ssh_user = "<cloud-provisioned user>"
+
+# 0|1 bastion nodes
+number_of_bastions = 0
+
+#flavor_bastion = "<UUID>"
+
+# standalone etcds
+number_of_etcd = 0
+
+# masters
+number_of_k8s_masters = 1
+
+number_of_k8s_masters_no_etcd = 0
+
+number_of_k8s_masters_no_floating_ip = 0
+
+number_of_k8s_masters_no_floating_ip_no_etcd = 0
+
+flavor_k8s_master = "<UUID>"
+
+# nodes
+number_of_k8s_nodes = 2
+
+number_of_k8s_nodes_no_floating_ip = 4
+
+#flavor_k8s_node = "<UUID>"
+
+# GlusterFS
+# either 0 or more than one
+#number_of_gfs_nodes_no_floating_ip = 0
+#gfs_volume_size_in_gb = 150
+# Container Linux does not support GlusterFS
+#image_gfs = "<image name>"
+# May be different from other nodes
+#ssh_user_gfs = "ubuntu"
+#flavor_gfs_node = "<UUID>"
+
+# networking
+network_name = "<network>"
+
+external_net = "<UUID>"
+
+subnet_cidr = "<cidr>"
+
+floatingip_pool = "<pool>"
+
+bastion_allowed_remote_ips = ["0.0.0.0/0"]