doc: Update for OpenStack Juno.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
Merge pull request #2854 from ceph/wip-doc-openstack-juno

doc: Update for OpenStack Juno.

New users working with Nova (Juno) noted that libvirt settings are now under a [libvirt] section, and truncate the leading libvirt_. Made subsections for Havana and Icehouse, added a new subsection for Juno.
doc: Added Key/Value store config reference to index.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Edited Key/Value store config reference.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
osd: cache pool: flush object ignoring cache min flush age when cache pool is full
Signed-off-by: Xinze Chi <xmdxcxz@gmail.com>
Merge pull request #2856 from XinzeChi/master

osd: cache pool: flush object ignoring cache min flush age when cache pool is full

Backport: giant, firefly
Reviewed-by: Sage Weil <sage@redhat.com>