plugable: switch API to Registry-based plugin discovery

Merge Registrar into Registry. Use the Registry instance of each plugin
module to discover plugins in the module instead of the global Registrar
instance.

This removes the side-effect of all plugins in a module being re-registered
every time the module is imported.

https://fedorahosted.org/freeipa/ticket/4739

Reviewed-By: David Kupka <dkupka@redhat.com>

ipatests/test_ipalib/test_plugable.py

@@ -98,9 +98,9 @@ class test_Plugin(ClassChecker):
         assert o.__islocked__()
 
 
-def test_Registrar():
+def test_Registry():
     """
-    Test the `ipalib.plugable.Registrar` class
+    Test the `ipalib.plugable.Registry` class
     """
     class Base1(object):
         pass
@@ -115,59 +115,49 @@ def test_Registrar():
     class plugin3(Base3):
         pass
 
-    # Test creation of Registrar:
-    r = plugable.Registrar()
+    # Test creation of Registry:
+    r = plugable.Registry()
 
     # Check that TypeError is raised trying to register something that isn't
     # a class:
     p = plugin1()
-    e = raises(TypeError, r, p)
+    e = raises(TypeError, r(), p)
     assert str(e) == 'plugin must be a class; got %r' % p
 
     # Check that registration works
-    r(plugin1)
-    assert len(r) == 1
-    assert plugin1 in r
-    assert r[plugin1] == dict(override=False)
+    r()(plugin1)
 
     # Check that DuplicateError is raised trying to register exact class
     # again:
-    e = raises(errors.PluginDuplicateError, r, plugin1)
+    e = raises(errors.PluginDuplicateError, r(), plugin1)
     assert e.plugin is plugin1
 
     # Check that overriding works
-    orig1 = plugin1
     class base1_extended(Base1):
         pass
     class plugin1(base1_extended):  # pylint: disable=function-redefined
         pass
-    r(plugin1, override=True)
-    assert len(r) == 2
-    assert plugin1 in r
-    assert r[plugin1] == dict(override=True)
+    r(override=True)(plugin1)
 
     # Test that another plugin can be registered:
-    r(plugin2)
-    assert len(r) == 3
-    assert plugin2 in r
-    assert r[plugin2] == dict(override=False)
+    r()(plugin2)
 
     # Setup to test more registration:
     class plugin1a(Base1):
         pass
-    r(plugin1a)
+    r()(plugin1a)
 
     class plugin1b(Base1):
         pass
-    r(plugin1b)
+    r()(plugin1b)
 
     class plugin2a(Base2):
         pass
-    r(plugin2a)
+    r()(plugin2a)
 
     class plugin2b(Base2):
         pass
-    r(plugin2b)
+    r()(plugin2b)
 
 
 class test_API(ClassChecker):