Add architecture validation to manifest lists that contain schema 1 manifests

Fixes https://jira.coreos.com/browse/QUAY-1266

image/docker/interfaces.py

@@ -38,6 +38,13 @@ class ManifestInterface(object):
         cannot be computed locally.
     """
 
+  @abstractmethod
+  def validate(self, content_retriever):
+    """ Performs validation of required assertions about the manifest. Raises a ManifestException
+        on failure.
+    """
+    pass
+
   @abstractmethod
   def get_layers(self, content_retriever):
     """ Returns the layers of this manifest, from base to leaf or None if this kind of manifest