Merge pull request #314 from gildub/instance_prov-allow-disk-0

Instances workflow: Allow flavors with disk size of 0

(cherry picked from commit 5598b27)

https://bugzilla.redhat.com/show_bug.cgi?id=1643042

app/models/manageiq/providers/openstack/cloud_manager/provision_workflow.rb

@@ -14,7 +14,8 @@ def allowed_instance_types(_options = {})
       minimum_memory_required = source.hardware.memory_mb_minimum.to_i * 1.megabyte
     end
     flavors.each_with_object({}) do |flavor, h|
-      next if flavor.root_disk_size < minimum_disk_required
+      # Allow flavors with 0 disk size: The instance will grow disk based upon image build definition
+      next if flavor.root_disk_size.positive? && flavor.root_disk_size < minimum_disk_required
       next if flavor.memory         < minimum_memory_required
       h[flavor.id] = display_name_for_name_description(flavor)
     end