Implement HEAD handler for v2/pkgs/tools/installed (required by frontend) (#844)

* add tests

* implement HEAD method (is used by the frontend).
Without this the server returns 405 when called with HEAD to `v2/pkgs/tools/installed`
This breaks the install of the tools

Author: umbynos

Diff for: design/pkgs.go

@@ -28,6 +28,13 @@ var _ = Service("tools", func() {
 		})
 	})
 
+	Method("installedhead", func() {
+		HTTP(func() {
+			HEAD("/pkgs/tools/installed")
+			Response(StatusOK)
+		})
+	})
+
 	Method("installed", func() {
 		Result(CollectionOf(Tool))
 		HTTP(func() {

Diff for: gen/http/cli/arduino_create_agent/cli.go

@@ -61,6 +61,16 @@ paths:
                         $ref: '#/definitions/ToolsInstallResponseBody'
             schemes:
                 - http
+        head:
+            tags:
+                - tools
+            summary: installedhead tools
+            operationId: tools#installedhead
+            responses:
+                "200":
+                    description: OK response.
+            schemes:
+                - http
     /pkgs/tools/installed/{packager}/{name}/{version}:
         delete:
             tags:

Diff for: gen/http/openapi.json

@@ -53,6 +53,14 @@ paths:
                                 - name: bossac
                                   packager: arduino
                                   version: 1.7.0-arduino3
+        head:
+            tags:
+                - tools
+            summary: installedhead tools
+            operationId: tools#installedhead
+            responses:
+                "200":
+                    description: OK response.
         post:
             tags:
                 - tools