Suppress pagination on non-tty glance index.

Fixes bug 978610.

Avoid the 'Fetch next page? [Y/n]' prompt interfering with
redirected output.

The native glance CLI will soon be superceeded by the new
python-glanceclient, however this patch could still be useful
to propogate from master to the stable diablo/essex branches.

Change-Id: I16bc6156d7c7e9ed27aabcaa51211060ec24a824

bin/glance

@@ -516,7 +516,11 @@ def _images_index(client, filters, limit, print_header=False, **kwargs):
                                     image['container_format'],
                                     image['size'])
 
-    if not options.force and len(images) == limit and \
+    # suppress pagination when output is redirected
+    suppress_pagination = (options.force or
+        (getattr(os, 'isatty') and not os.isatty(sys.stdout.fileno())))
+
+    if not suppress_pagination and len(images) == limit and \
        not user_confirm("Fetch next page?", True):
         return SUCCESS