Let the docker variable be used to specify which subdirs to look in

If you don't specify the subdir, all top level dirs are automatically
scanned. Alternatively, following the example, you can specify exactly
which Dockerfiles you want to have build.

examples/docker-subdirs.yaml

@@ -0,0 +1,33 @@
+---
+:domain: example.com
+:network: 192.168.123.0/24
+:image: centos-7.1-docker
+:boxurlprefix: ''
+:sync: rsync
+:folder: ''
+:extern:
+- type: git
+  system: docker
+  repository: https://github.com/fedora-cloud/Fedora-Dockerfiles
+  directory: Fedora-Dockerfiles
+:puppet: false
+:classes: []
+:docker:
+  images: []
+  files:
+  - Fedora-Dockerfiles/apache
+  - Fedora-Dockerfiles/wordpress
+:kubernetes: false
+:ansible: []
+:playbook: []
+:cachier: false
+:vms: []
+:namespace: omv
+:count: 1
+:username: ''
+:password: ''
+:poolid: true
+:repos: []
+:update: false
+:comment: sub folder simple docker file build example
+:reallyrm: false

vagrant/Vagrantfile

@@ -604,6 +604,7 @@ if extern.length > 0
 				repository = File.expand_path(repository)
 			end
 			directory = i.fetch('directory', nil)
+			directory = directory[0, (directory.index('/', 1).nil?? directory.length : directory.index('/', 1))]
 			branch = i.fetch('branch', nil)
 			if repository.nil? or directory.nil?
 				next
@@ -994,7 +995,14 @@ Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
 
 			# docker build
 			if vm_docker	# for any value that is not false
-				Dir.glob(docker_basedir+'*').each do |dd|
+				dlist = Dir.glob(docker_basedir+'*')
+				if vm_docker.is_a?(Hash)
+					dfiles = vm_docker.fetch('files', nil)
+					if dfiles.is_a?(Array)
+						dlist = vm_docker['files'].map{|dfile| File.join(docker_basedir, dfile)}
+					end
+				end
+				dlist.each do |dd|
 					if not File.directory?(dd)
 						next	# invalid, skip
 					end