Install Guide: Fix SUSE neutron-server setup

On SLES and openSUSE the neutron-server service is called
openstack-neutron.

Change-Id: I426dbb131b570750508c3e1b0fa2d2c892c51a91
backport: havana
(cherry picked from commit b6ec3604cca53441f9e80eca86336d104028503a)