always pass in the full plugin path to dicovery

Discovery no longer tries to walk into OS_ARCH dirs, so always pass in
the full search path.

command/command.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"runtime"
 
 	"github.com/hashicorp/terraform/terraform"
 	"github.com/mitchellh/cli"
@@ -19,10 +20,13 @@ const DefaultDataDir = ".terraform"
 // of directories supplied by the user with the `-plugin-dir` flag during init.
 const PluginPathFile = "plugin_path"
 
+// pluginMachineName is the directory name used in new plugin paths.
+const pluginMachineName = runtime.GOOS + "_" + runtime.GOARCH
+
 // DefaultPluginVendorDir is the location in the config directory to look for
 // user-added plugin binaries. Terraform only reads from this path if it
 // exists, it is never created by terraform.
-const DefaultPluginVendorDir = "terraform.d/plugins"
+const DefaultPluginVendorDir = "terraform.d/plugins/" + pluginMachineName
 
 // DefaultStateFilename is the default filename used for the state file.
 const DefaultStateFilename = "terraform.tfstate"

command/init_test.go

@@ -519,11 +519,7 @@ func TestInit_findVendoredProviders(t *testing.T) {
 	if err := os.MkdirAll(c.pluginDir(), 0755); err != nil {
 		t.Fatal(err)
 	}
-	vendorMachineDir := filepath.Join(
-		DefaultPluginVendorDir,
-		fmt.Sprintf("%s_%s", runtime.GOOS, runtime.GOARCH),
-	)
-	if err := os.MkdirAll(vendorMachineDir, 0755); err != nil {
+	if err := os.MkdirAll(DefaultPluginVendorDir, 0755); err != nil {
 		t.Fatal(err)
 	}
 
@@ -534,7 +530,7 @@ func TestInit_findVendoredProviders(t *testing.T) {
 		t.Fatal(err)
 	}
 	// the vendor path
-	greaterThanPath := filepath.Join(vendorMachineDir, "terraform-provider-greater_than_v2.3.4_x4")
+	greaterThanPath := filepath.Join(DefaultPluginVendorDir, "terraform-provider-greater_than_v2.3.4_x4")
 	if err := ioutil.WriteFile(greaterThanPath, []byte("test bin"), 0755); err != nil {
 		t.Fatal(err)
 	}