Rewrite link parsing for finding v2 schemas

What we called 'links' are no longer returned in a container of
objects, they are top-level entity attribtues. This fixes the
parsing of the entities to look in the correct place when trying
to locate a specific schema.

Add a helper for printing to stderr and exiting with a non-zero
exit code.

Map 'name' to 'Attribute' when explaining a schema.

Related to bp glance-client-v2

Change-Id: Ib98e912a7af0bb570b4fd738733edd9b837d1a05

glanceclient/common/utils.py

@@ -14,6 +14,7 @@
 #    under the License.
 
 import os
+import sys
 import uuid
 
 import prettytable
@@ -47,7 +48,7 @@ def print_list(objs, fields, formatters={}):
                 row.append(formatters[field](o))
             else:
                 field_name = field.lower().replace(' ', '_')
-                data = getattr(o, field_name, '')
+                data = getattr(o, field_name, None) or ''
                 row.append(data)
         pt.add_row(row)
 
@@ -123,3 +124,9 @@ def import_versioned_module(version, submodule=None):
     if submodule:
         module = '.'.join((module, submodule))
     return importutils.import_module(module)
+
+
+def exit(msg=''):
+    if msg:
+        print >> sys.stderr, msg
+    sys.exit(1)