Support master_lb_enabled attribute for cluster resource

[dniasoff]

Code copied for https://github.com/terraform-provider-openstack/terraform-provider-openstack/pull/1136

[theopenlab-ci[bot]]

Build failed.

• terraform-provider-openstack-unittest-foo : FAILURE in 2m 36s
• terraform-provider-openstack-acceptance-test-foo : FAILURE in 1h 52m 56s
• terraform-provider-openstack-acceptance-test-admin-foo : FAILURE in 1h 51m 34s

[ozerovandrei]

That won't work until https://github.com/gophercloud/gophercloud/issues/2117 is resolved in the upstream library.

c.MasterLBEnabled undefined (type *clusters.Cluster has no field or method MasterLBEnabled)
s.MasterLBEnabled undefined (type *clusters.Cluster has no field or method MasterLBEnabled)