Tiny little last-minute changes

operations/backup -- made this a top-level head and fixed the
bullet lists

terminology:
amqp -- fixed bad reference list formatting
availability-zone -- fixed bad ref to host-aggregates
ceilometer -- fixed bad reference list formatting
ha -- show single-controller HA mode as available in 5.1
hadoop -- added link to Sahara article
host-aggregates -- fixed bad tag
sahara -- filled in description for sahara-plan and moved it

Change-Id: Ie1f8138ead170085f38b6730189ab393942674d7