core: Vagrantfile must be file [GH-2216]

CHANGELOG.md

@@ -19,6 +19,8 @@ BUG FIXES:
     works. [GH-2196]
   - core: Don't try to be clever about deleting the machine state
     directory anymore. Manually done in destroy actions. [GH-2201]
+  - core: Find the root Vagrantfile only if Vagrantfile is a file, not
+    a directory. [GH-2216]
   - guests/linux: Try `id -g` in addition to `getent` for mounting
     VirtualBox shared folders [GH-2197]
   - hosts/arch: NFS exporting works properly, no exceptions. [GH-2161]

lib/vagrant/environment.rb

@@ -709,7 +709,7 @@ module Vagrant
       filenames ||= ["Vagrantfile", "vagrantfile"]
       filenames.each do |vagrantfile|
         current_path = search_path.join(vagrantfile)
-        return current_path if current_path.exist?
+        return current_path if current_path.file?
       end
 
       nil