Simplify placement.microversion:_fully_qualified_name

_fully_qualified_name was copied from Twisted. The original
version does more than Placement needs. We only need to
handle module-level classes and functions (and really only
functions). No nested of those, nor object methods in any
form.

This is because we only use the method for finding the
right microversioned handler of a method with the same
name and placement HTTP handlers are universally functions.

The previous version of the method had code that was never
called. Here, that dead code is removed and the remainder
is simplified.

If it is called incorrectly there will be an (intentionally)
untrapped TypeError during running of the tests.

N.B.: This was discovered while reviewing coverage data.

Change-Id: Id8f96801116818dda6c68c301619aee185e8fbff

placement/microversion.py

@@ -99,33 +99,19 @@ def min_version_string():
     return VERSIONS[0]
 
 
-# From twisted
+# Based on code in twisted
 # https://github.com/twisted/twisted/blob/trunk/twisted/python/deprecate.py
-def _fully_qualified_name(obj):
-    """Return the fully qualified name of a module, class, method or function.
-
-    Classes and functions need to be module level ones to be correctly
-    qualified.
+def _fully_qualified_name(handler):
+    """Return the name of a function or class used as an HTTP API handler,
+    qualified by module name.
     """
-    try:
-        name = obj.__qualname__
-    except AttributeError:
-        name = obj.__name__
+    if inspect.isfunction(handler) or inspect.isclass(handler):
+        module_name = handler.__module__
+        return "%s.%s" % (module_name, handler.__name__)
 
-    if inspect.isclass(obj) or inspect.isfunction(obj):
-        moduleName = obj.__module__
-        return "%s.%s" % (moduleName, name)
-    elif inspect.ismethod(obj):
-        try:
-            cls = obj.im_class
-        except AttributeError:
-            # Python 3 eliminates im_class, substitutes __module__ and
-            # __qualname__ to provide similar information.
-            return "%s.%s" % (obj.__module__, obj.__qualname__)
-        else:
-            className = _fully_qualified_name(cls)
-            return "%s.%s" % (className, name)
-    return name
+    # We got an object method or module. This is a coding error.
+    raise TypeError("_fully_qualified_name received bad handler type. "
+                    "Module-level class or function required.")
 
 
 def _find_method(f, version, status_code):