Correct name of Ceilometer central agent service for Fedora and EL

Fedora and EL-based operating systems use the name
"openstack-ceilometer-central" for this service rather than
"openstack-ceilometer-agent-central.

As such while there is overlap with the instructions for openSUSE and
SLES this slight difference needs to be accounted for.

Change-Id: I8f922cafd35e1eedfa8d00f14cf07acbeefe842f
backport: havana
Closes-Bug: #1252265
(cherry picked from commit aaf0480fe3a0f6473ecfc238e04c3e57fe900d09)
Fix GroupAffinityFilter and GroupAntiAffinityFilter doc

The hint key is 'group' and not 'group_hosts', and the hint value is an
arbitrary value and not an instance UUID.

Change-Id: If2a034f727e09172dc5bf3d42a9c205df449ca72
Closes-Bug: #1223242
backport: havana
(cherry picked from commit 5b9d40cf28c69662cb9d27cd55a513f00adfcdaa)
Merge "Correct name of Ceilometer central agent service for Fedora and EL" into stable/havana
Merge "Fix GroupAffinityFilter and GroupAntiAffinityFilter doc" into stable/havana