Disable loading identical Vagrantfile twice from same dir

Prior to this commit, if a user set the env var VAGRANT_HOME to be the
same directory where the project home is, Vagrant would load that file
twice and merge its config. This caused various provisioner and other
provider blocks to unexpectedly run twice. This commit updates the
config loader to look and see if the `:root` and `:home` procs are
equal, and if so, removes the `:home` object so that it isn't loaded and
duplicated. This commit however does not prevent duplicate loading if an
identical Vagrantfile exists in the home and project dir if those
locations are different.

lib/vagrant/config/loader.rb

@@ -101,6 +101,18 @@ module Vagrant
         warnings = []
         errors   = []
 
+        if !@sources[:root].nil? && @sources[:root].eql?(@sources[:home])
+          # Vagrants home dir is set to the same dir as its project directory
+          # so we don't want to load and merge the same Vagrantfile config
+          # and execute its settings/procs twice
+          #
+          # Note: This protection won't work if there are two separate but
+          # identical Vagrantfiles in the home and project dir
+          @logger.info("Duplicate Vagrantfile config objects detected in :root and :home.")
+          @sources.delete(:home)
+          @logger.info("Removed :home config from being loaded")
+        end
+
         order.each do |key|
           next if !@sources.key?(key)
 

test/unit/vagrant/config/loader_test.rb

@@ -23,7 +23,7 @@ describe Vagrant::Config::Loader do
       end
 
       def self.merge(old, new)
-        old.merge(new)
+        old.merge(new) {|key, oldval, newval| oldval.concat(newval)}
       end
     end
   end
@@ -177,6 +177,25 @@ describe Vagrant::Config::Loader do
       end
     end
 
+    it "should discard duplicate configs if :home and :root are the same" do
+      proc = Proc.new do |config|
+        config[:foo] = ["yep"]
+      end
+
+      order = [:root, :home]
+
+      instance.set(:root, [[current_version, proc]])
+      instance.set(:home, [[current_version, proc]])
+
+      result, warnings, errors = instance.load(order)
+
+      # Verify the config result
+      expect(result[:foo]).to eq(["yep"])
+      expect(result[:foo].size).to eq(1)
+      expect(warnings).to eq([])
+      expect(errors).to eq([])
+    end
+
     it "should only load configuration files once" do
       $_config_data = 0