Installs 64bit chef on windows if available

Resolves #3847

- Changes linux install url to new omnitruck.chef.io url. 
- Changes powershell install to use omnitruck url instead of hard coded to 32bit msi install.

provisioner/chef-solo/provisioner.go

@@ -28,12 +28,12 @@ type guestOSTypeConfig struct {
 var guestOSTypeConfigs = map[string]guestOSTypeConfig{
 	provisioner.UnixOSType: guestOSTypeConfig{
 		executeCommand: "{{if .Sudo}}sudo {{end}}chef-solo --no-color -c {{.ConfigPath}} -j {{.JsonPath}}",
-		installCommand: "curl -L https://www.chef.io/chef/install.sh | {{if .Sudo}}sudo {{end}}bash",
+		installCommand: "curl -L  https://omnitruck.chef.io/install.sh | {{if .Sudo}}sudo {{end}}bash",
 		stagingDir:     "/tmp/packer-chef-client",
 	},
 	provisioner.WindowsOSType: guestOSTypeConfig{
 		executeCommand: "c:/opscode/chef/bin/chef-solo.bat --no-color -c {{.ConfigPath}} -j {{.JsonPath}}",
-		installCommand: "powershell.exe -Command \"(New-Object System.Net.WebClient).DownloadFile('http://chef.io/chef/install.msi', 'C:\\Windows\\Temp\\chef.msi');Start-Process 'msiexec' -ArgumentList '/qb /i C:\\Windows\\Temp\\chef.msi' -NoNewWindow -Wait\"",
+		installCommand: "powershell.exe -Command \". { iwr -useb https://omnitruck.chef.io/install.ps1 } | iex; install\"",
 		stagingDir:     "C:/Windows/Temp/packer-chef-client",
 	},
 }