Also follow HELM_PLUGINS when installing from http

This is effectively <https://github.com/helm/helm/pull/10008> but for the overridden case of `Path()` in `pkg/plugins/installer/http_installer.go`. Well slightly simpler because it can just use the directory already in `base`.

The test is copied nearly wholesale from that PR.

Signed-off-by: Graham Reed <greed@7deadly.org>

pkg/plugin/installer/http_installer.go

@@ -159,7 +159,7 @@ func (i HTTPInstaller) Path() string {
 	if i.base.Source == "" {
 		return ""
 	}
-	return helmpath.DataPath("plugins", i.PluginName)
+	return filepath.Join(i.base.PluginsDirectory, i.PluginName)
 }
 
 // cleanJoin resolves dest as a subpath of root.

pkg/plugin/installer/http_installer_test.go

@@ -348,3 +348,38 @@ func TestMediaTypeToExtension(t *testing.T) {
 		}
 	}
 }
+
+func TestHttpInstallerPath(t *testing.T) {
+	tests := []struct {
+		source         string
+		pluginName     string
+		helmPluginsDir string
+		expectPath     string
+	}{
+		{
+			source:         "",
+			pluginName:     "not-used",
+			helmPluginsDir: "/helm/data/plugins",
+			expectPath:     "",
+		}, {
+			source:         "https://github.com/jkroepke/helm-secrets",
+			pluginName:     "helm-http-plugin",
+			helmPluginsDir: "/helm/data/plugins",
+			expectPath:     "/helm/data/plugins/helm-http-plugin",
+		},
+	}
+
+	for _, tt := range tests {
+
+		os.Setenv("HELM_PLUGINS", tt.helmPluginsDir)
+		ins := &HTTPInstaller{
+			PluginName: tt.pluginName,
+			base:       newBase(tt.source),
+		}
+		insPath := ins.Path()
+		if insPath != tt.expectPath {
+			t.Errorf("expected name %s, got %s", tt.expectPath, insPath)
+		}
+		os.Unsetenv("HELM_PLUGINS")
+	}
+}