Remove HEAD methods from GET routes

Although not 100% correct following RESTful definition, we drop them as
it only introduces confusion in our case.

Author: alvarolopez

deepaas/api/v2/__init__.py

@@ -38,7 +38,7 @@ def get_app(enable_train=True, enable_predict=True):
 
     v2_debug.setup_debug()
 
-    APP.router.add_get('/', get_version, name="v2")
+    APP.router.add_get('/', get_version, name="v2", allow_head=False)
     v2_debug.setup_routes(APP)
     v2_model.setup_routes(APP)
     v2_train.setup_routes(APP, enable=enable_train)

deepaas/api/v2/debug.py

@@ -94,4 +94,4 @@ async def get(request, wsk_args=None):
 
 
 def setup_routes(app):
-    app.router.add_get("/debug/", get)
+    app.router.add_get("/debug/", get, allow_head=False)

deepaas/api/v2/models.py

@@ -88,11 +88,13 @@ async def get(self, request, wsk_args=None):
 
 
 def setup_routes(app):
-    app.router.add_get("/models/", index)
+    app.router.add_get("/models/", index, allow_head=False)
 
     # In the next lines we iterate over the loaded models and create the
     # different resources for each model. This way we can also load the
     # expected parameters if needed (as in the training method).
     for model_name, model_obj in model.V2_MODELS.items():
         hdlr = _get_handler(model_name, model_obj)
-        app.router.add_get("/models/%s/" % model_name, hdlr.get)
+        app.router.add_get("/models/%s/" % model_name,
+                           hdlr.get,
+                           allow_head=False)

deepaas/api/v2/train.py

@@ -140,8 +140,12 @@ def setup_routes(app, enable=True):
         else:
             hdlr = utils.NotEnabledHandler()
         app.router.add_post("/models/%s/train/" % model_name, hdlr.post)
-        app.router.add_get("/models/%s/train/" % model_name, hdlr.index)
-        app.router.add_get("/models/%s/train/{uuid}" % model_name, hdlr.get)
+        app.router.add_get("/models/%s/train/" % model_name,
+                           hdlr.index,
+                           allow_head=False)
+        app.router.add_get("/models/%s/train/{uuid}" % model_name,
+                           hdlr.get,
+                           allow_head=False)
         app.router.add_delete(
             "/models/%s/train/{uuid}" % model_name,
             hdlr.delete