Convert root controller to plain controller

The RestController._route method[1] contains a lot of logic which
exists to support implementing CRUD APIs, none of which is required to
server / and /v1.

This change converts the RestController based root controller with a
simple object based controller. This results in a shorter code path
for every API request.

The path / is handled by the index method, with the *args length check
returning a 404 to be consistent with the previous behaviour of
returning a 404 for a request like //v1

The _route method is replaced with a _lookup[2] method to handle paths
which are missing the v1 prefix (and to curate the trailing slash from
the path, which was been done by the RestController).

[1] https://github.com/pecan/pecan/blob/master/pecan/rest.py#L103

Change-Id: Ia962f9bf53af12fb308e3d66eff114b302638714
Story: 1651346
Task: 10551

ironic/api/controllers/root.py

@@ -15,13 +15,15 @@
 # under the License.
 
 import pecan
-from pecan import rest
 
 from ironic.api.controllers import v1
 from ironic.api.controllers import version
 from ironic.api import method
 
 
+V1 = v1.Controller()
+
+
 def root():
     return {
         'name': "OpenStack Ironic API",
@@ -32,22 +34,32 @@ def root():
     }
 
 
-class RootController(rest.RestController):
-
-    v1 = v1.Controller()
+class RootController(object):
 
     @method.expose()
-    def get(self):
+    def index(self, *args):
+        if args:
+            pecan.abort(404)
         return root()
 
     @pecan.expose()
-    def _route(self, args, request=None):
+    def _lookup(self, primary_key, *remainder):
         """Overrides the default routing behavior.
 
         It redirects the request to the default version of the ironic API
         if the version number is not specified in the url.
         """
 
-        if args[0] and args[0] != version.ID_VERSION1:
-            args = [version.ID_VERSION1] + args
-        return super(RootController, self)._route(args, request)
+        # support paths which are missing the first version element
+        if primary_key and primary_key != version.ID_VERSION1:
+            remainder = [primary_key] + list(remainder)
+
+        # remove any trailing /
+        if remainder and not remainder[-1]:
+            remainder = remainder[:-1]
+
+        # but ensure /v1 goes to /v1/
+        if not remainder:
+            remainder = ['']
+
+        return V1, remainder