pkg/terraform/exec/plugins: vendor in random and local tf provider

The random provider is needed for azure to generate a storage
account name that is unique across azure.
storage account names also have extra naming restrictions.
is used to keep this in the package and avoid passing an extra
parameter as a variable.

The local provider is necessary to upload the ignition file to
azure storage because the azure provider does not support
binary upload. we need to create a file and pass it to the blob
upload resource instead.

tf blob storage resource : https://www.terraform.io/docs/providers/azurerm/r/storage_blob.html
storage naming limits : https://docs.microsoft.com/en-us/azure/architecture/best-practices/naming-conventions#storage

pkg/terraform/exec/plugins/Gopkg.toml

@@ -52,3 +52,7 @@ ignored = [
 [[override]]
   name = "github.com/hashicorp/go-azure-helpers"
   version = "0.3.2"
+
+[[constraint]]
+  name = "github.com/terraform-providers/terraform-provider-random"
+  version = "2.1.1"

pkg/terraform/exec/plugins/azure.go

@@ -3,13 +3,27 @@ package plugins
 import (
 	"github.com/hashicorp/terraform/plugin"
 	"github.com/terraform-providers/terraform-provider-azurerm/azurerm"
+	"github.com/terraform-providers/terraform-provider-local/local"
+	"github.com/terraform-providers/terraform-provider-random/random"
 )
 
 func init() {
-	exec := func() {
+	azurermProvider := func() {
 		plugin.Serve(&plugin.ServeOpts{
 			ProviderFunc: azurerm.Provider,
 		})
 	}
-	KnownPlugins["terraform-provider-azurerm"] = exec
+	localProvider := func() {
+		plugin.Serve(&plugin.ServeOpts{
+			ProviderFunc: local.Provider,
+		})
+	}
+	randomProvider := func() {
+		plugin.Serve(&plugin.ServeOpts{
+			ProviderFunc: random.Provider,
+		})
+	}
+	KnownPlugins["terraform-provider-azurerm"] = azurermProvider
+	KnownPlugins["terraform-provider-local"] = localProvider
+	KnownPlugins["terraform-provider-random"] = randomProvider
 }