Migrate Nuage CloudSubnet default type to new subclass

Nuage inventory was recently updated to fetch two types of CloudSubnets:

```
- ManageIQ::Providers::Nuage::NetworkManager::CloudSubnetL3
- ManageIQ::Providers::Nuage::NetworkManager::CloudSubnetL2
```

Before only CloudSubnetL3 were inventoried using default type
CloudSubnet. With this migration we make sure that this default
type is converted to CloudSubnetL3 type because persister won't
modify STI type per se.

Signed-off-by: Miha Pleško <[email protected]>

db/migrate/20180607084710_nuage_subclass_l3_cloud_subnet.rb

@@ -0,0 +1,19 @@
+class NuageSubclassL3CloudSubnet < ActiveRecord::Migration[5.0]
+  class CloudSubnet < ActiveRecord::Base
+    self.inheritance_column = :_type_disabled
+  end
+
+  def up
+    say_with_time('Migrating Nuage default subnet type to L3 subnet subclass') do
+      CloudSubnet.where(:type => 'ManageIQ::Providers::Nuage::NetworkManager::CloudSubnet')
+                 .update_all(:type => 'ManageIQ::Providers::Nuage::NetworkManager::CloudSubnetL3')
+    end
+  end
+
+  def down
+    say_with_time('Reverting Nuage L3 subnet subclass to default subnet type') do
+      CloudSubnet.where(:type => 'ManageIQ::Providers::Nuage::NetworkManager::CloudSubnetL3')
+                 .update_all(:type => 'ManageIQ::Providers::Nuage::NetworkManager::CloudSubnet')
+    end
+  end
+end

spec/migrations/20180607084710_nuage_subclass_l3_cloud_subnet_spec.rb

@@ -0,0 +1,45 @@
+require_migration
+
+describe NuageSubclassL3CloudSubnet do
+  let(:subnet_stub) { migration_stub :CloudSubnet }
+
+  migration_context :up do
+    it 'migrates base Nuage type' do
+      subnet = subnet_stub.create!(:type => 'ManageIQ::Providers::Nuage::NetworkManager::CloudSubnet')
+
+      migrate
+      subnet.reload
+
+      expect(subnet.type).to eql('ManageIQ::Providers::Nuage::NetworkManager::CloudSubnetL3')
+    end
+
+    it 'doesnt modify other subnets' do
+      subnet = subnet_stub.create!(:type => 'CloudSubnet')
+
+      migrate
+      subnet.reload
+
+      expect(subnet.type).to eql('CloudSubnet')
+    end
+  end
+
+  migration_context :down do
+    it 'restores base Nuage type' do
+      subnet = subnet_stub.create!(:type => 'ManageIQ::Providers::Nuage::NetworkManager::CloudSubnetL3')
+
+      migrate
+      subnet.reload
+
+      expect(subnet.type).to eql('ManageIQ::Providers::Nuage::NetworkManager::CloudSubnet')
+    end
+
+    it 'doesnt modify other subnets' do
+      subnet = subnet_stub.create!(:type => 'CloudSubnet')
+
+      migrate
+      subnet.reload
+
+      expect(subnet.type).to eql('CloudSubnet')
+    end
+  end
+end