ensure prefix in plugin loading to avoid conflicts

when using 'all' to load all plugins were ending in main namespace
creating conflicts with each other and random modulesr
 i.e. when trying to access json callback we were getting json 'parsing' lib

lib/ansible/plugins/__init__.py

@@ -329,13 +329,18 @@ class PluginLoader:
     __contains__ = has_plugin
 
     def _load_module_source(self, name, path):
-        if name in sys.modules:
-            # See https://github.com/ansible/ansible/issues/13110
-            return sys.modules[name]
+
+        # avoid collisions across plugins
+        full_name = '.'.join([self.package, name])
+
+        if full_name in sys.modules:
+            # Avoids double loading, See https://github.com/ansible/ansible/issues/13110
+            return sys.modules[full_name]
+
         with warnings.catch_warnings():
             warnings.simplefilter("ignore", RuntimeWarning)
             with open(path, 'rb') as module_file:
-                module = imp.load_source(name, path, module_file)
+                module = imp.load_source(full_name, path, module_file)
         return module
 
     def get(self, name, *args, **kwargs):
@@ -350,7 +355,7 @@ class PluginLoader:
             return None
 
         if path not in self._module_cache:
-            self._module_cache[path] = self._load_module_source('.'.join([self.package, name]), path)
+            self._module_cache[path] = self._load_module_source(name, path)
             found_in_cache = False
 
         obj = getattr(self._module_cache[path], self.class_name)