Sync importutils changes from openstack-common

Syncs the following changes from stable/folsom:

 769ec65 Don't trap then re-raise ImportError.
 8c74b37 Improve exception from importutils.import_class().
 1fb2361 add import_object_ns function

Change-Id: Ib6046181ec4712702c30c8a8e938fc9a21b1a594

glanceclient/openstack/common/importutils.py

@@ -20,6 +20,7 @@ Import related utilities and helper functions.
 """
 
 import sys
+import traceback
 
 
 def import_class(import_str):
@@ -28,9 +29,10 @@ def import_class(import_str):
     try:
         __import__(mod_str)
         return getattr(sys.modules[mod_str], class_str)
-    except (ImportError, ValueError, AttributeError), exc:
+    except (ValueError, AttributeError), exc:
         raise ImportError('Class %s cannot be found (%s)' %
-                (class_str, str(exc)))
+                          (class_str,
+                           traceback.format_exception(*sys.exc_info())))
 
 
 def import_object(import_str, *args, **kwargs):
@@ -38,6 +40,19 @@ def import_object(import_str, *args, **kwargs):
     return import_class(import_str)(*args, **kwargs)
 
 
+def import_object_ns(name_space, import_str, *args, **kwargs):
+    """
+    Import a class and return an instance of it, first by trying
+    to find the class in a default namespace, then failing back to
+    a full path if not found in the default namespace.
+    """
+    import_value = "%s.%s" % (name_space, import_str)
+    try:
+        return import_class(import_value)(*args, **kwargs)
+    except ImportError:
+        return import_class(import_str)(*args, **kwargs)
+
+
 def import_module(import_str):
     """Import a module."""
     __import__(import_str)