Remove Icehouse and Juno content from sitemap
Remove Icehouse and Juno content from sitemap

Icehouse and Juno docs should not be accesed, so this updates the sitemap
generator tool to skip them. The sitemap can then be regenerated.

Partial-Bug: #1602647
Change-Id: I3117b114881c3a12b6a1a9565a0a720c9c8678b1

openstack/openstack-doc-tools,openstack/openstack-doc-tools