Ignore files created by Sphinx build

Change-Id: I46f34d9320ce39977facff705c52d272a160220f
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Remove references to clean arg from cache-manage

The usage message for glance-cache-manage lists "clean" as an available
command, but this functionality is part of a separate tool,
glance-cache-cleaner.

Remove any references to this to avoid confusion.

DocImpact
Fixes bug 1189451

Change-Id: I2aba8164ab9ef0c3bef31870cb3771233a722d27
Merge "Remove references to clean arg from cache-manage"
Merge "Ignore files created by Sphinx build"