Update openstack.yml (#4795)

Fix comment style

inventory/sample/group_vars/all/openstack.yml

-# # When OpenStack is used, Cinder version can be explicitly specified if autodetection fails (Fixed in 1.9: https://github.com/kubernetes/kubernetes/issues/50461)
+## When OpenStack is used, Cinder version can be explicitly specified if autodetection fails (Fixed in 1.9: https://github.com/kubernetes/kubernetes/issues/50461)
 # openstack_blockstorage_version: "v1/v2/auto (default)"
 # openstack_blockstorage_ignore_volume_az: yes
-# # When OpenStack is used, if LBaaSv2 is available you can enable it with the following 2 variables.
+## When OpenStack is used, if LBaaSv2 is available you can enable it with the following 2 variables.
 # openstack_lbaas_enabled: True
 # openstack_lbaas_subnet_id: "Neutron subnet ID (not network ID) to create LBaaS VIP"
-# # To enable automatic floating ip provisioning, specify a subnet.
+## To enable automatic floating ip provisioning, specify a subnet.
 # openstack_lbaas_floating_network_id: "Neutron network ID (not subnet ID) to get floating IP from, disabled by default"
-# # Override default LBaaS behavior
+## Override default LBaaS behavior
 # openstack_lbaas_use_octavia: False
 # openstack_lbaas_method: "ROUND_ROBIN"
 # openstack_lbaas_provider: "haproxy"