The openstack Ussuri and Victoria versions no longer support the
Centos7 and pyrhon2 environment packages. Correct the missing
problems in the latest document
Change-Id: I60787243fdc6ed2741522355ec79970bdb912f41
(cherry picked from commit 35dea07897)
(cherry picked from commit 77be4c6c69)
(cherry picked from commit 3258e49a5e)