Get default provider from go side

For now the go side will just return a hard coded value for the
default provider. It should be implementing the algorithm defined
at https://www.vagrantup.com/docs/providers/basic_usage.html#default-provider

internal/core/project.go

@@ -100,8 +100,9 @@ func (p *Project) DefaultPrivateKey() (path path.Path, err error) {
 
 // DefaultProvider implements core.Project
 func (p *Project) DefaultProvider() (name string, err error) {
-	// TODO
-	return
+	// TODO: This needs to implement the default provider algorithm
+	// from https://www.vagrantup.com/docs/providers/basic_usage.html#default-provider
+	return "virtualbox", nil
 }
 
 // Home implements core.Project

lib/vagrant/environment/remote.rb

@@ -24,8 +24,8 @@ module Vagrant
         opts[:ui_class] ||= UI::Remote
 
         @cwd = Pathname.new(@client.cwd)
-        @home_path = @client.respond_to?(:home) && Pathname.new(@client.home)
-        @vagrantfile_name = @client.respond_to?(:vagrantfile_name) && [@client.vagrantfile_name]
+        @home_path = Pathname.new(@client.home)
+        @vagrantfile_name = Array(@client.vagrantfile_name)
         @ui = opts.fetch(:ui, opts[:ui_class].new(@client.ui))
         @local_data_path = Pathname.new(@client.local_data)
         @boxes_path = @home_path && @home_path.join("boxes")
@@ -101,11 +101,9 @@ module Vagrant
         @config_loader
       end
 
-      # TODO: for now don't interfere with the default_provider method
-      #  once it is implemented on the Go side then this can be uncommented
-      # def default_provider(**opts)
-      #   client.default_provider
-      # end
+      def default_provider(**opts)
+        client.default_provider.to_sym
+      end
 
       # Returns the host object associated with this environment.
       #