adding plugin dir init option

DOCS.md

@@ -202,6 +202,9 @@ init_options.lock
 init_options.lock-timeout
 : Duration to wait for a state lock. Default `0s`.
 
+init_options.plugin-dir
+: Local path to use terraform plugins from. Default is `""` which will pull from upstream Terraform.
+
 vars
 : a map of variables to pass to the Terraform `plan` and `apply` commands.
 Each value is passed as a `-var <key>=<value>` option.

plugin.go

@@ -45,6 +45,7 @@ type (
 		BackendConfig []string `json:"backend-config"`
 		Lock          *bool    `json:"lock"`
 		LockTimeout   string   `json:"lock-timeout"`
+		PluginDir	  string   `json:"plugin-dir`
 	}
 
 	// Plugin represents the plugin instance to be executed
@@ -205,6 +206,11 @@ func initCommand(config InitOptions) *exec.Cmd {
 		args = append(args, fmt.Sprintf("-lock-timeout=%s", config.LockTimeout))
 	}
 
+	// "" is default in TF
+	if config.PluginDir != "" {
+		args = append(args, fmt.Sprintf("-plugin-dir=%s", config.PluginDir))
+	}
+
 	// Fail Terraform execution on prompt
 	args = append(args, "-input=false")