Prevent duplicate role insertion into roles: (#50552)

* Corner case in which import_role would add another instance of a role with the same signature into roles: when it already existed there.

  roles:
	- name: a
  tasks:
       - import_role: name=a

  would execute role 'a' 3 times instead of the intended 2 (x2 in roles: phase +1 in tasks:)

* added tests

lib/ansible/playbook/role/__init__.py

@@ -149,6 +149,9 @@ class Role(Base, Become, Conditional, Taggable):
                 params['from_files'] = from_files
             if role_include.vars:
                 params['vars'] = role_include.vars
+
+            params['from_include'] = from_include
+
             hashed_params = hash_params(params)
             if role_include.role in play.ROLE_CACHE:
                 for (entry, role_obj) in iteritems(play.ROLE_CACHE[role_include.role]):