Add scoring engines to database and API layers

A Scoring Module needs to expose a list of available
scoring engines through API and Watcher CLI. This list
is stored in database and synchronized by Decision Engine.

Partially-Implements: blueprint scoring-module
Change-Id: I32168adeaf34fd12a731204c5b58fe68434ad087
APIImpact

watcher/api/controllers/v1/collection.py

@@ -35,7 +35,7 @@ class Collection(base.APIBase):
         """Return whether collection has more items."""
         return len(self.collection) and len(self.collection) == limit
 
-    def get_next(self, limit, url=None, **kwargs):
+    def get_next(self, limit, url=None, marker_field="uuid", **kwargs):
         """Return a link to the next subset of the collection."""
         if not self.has_next(limit):
             return wtypes.Unset
@@ -44,7 +44,7 @@ class Collection(base.APIBase):
         q_args = ''.join(['%s=%s&' % (key, kwargs[key]) for key in kwargs])
         next_args = '?%(args)slimit=%(limit)d&marker=%(marker)s' % {
             'args': q_args, 'limit': limit,
-            'marker': getattr(self.collection[-1], "uuid")}
+            'marker': getattr(self.collection[-1], marker_field)}
 
         return link.Link.make_link('next', pecan.request.host_url,
                                    resource_url, next_args).href