For some providers (such as upcoming Linode support), some NICs may have
multiple IP addresses. (In the case of Linode, the only NIC has a public
and private IP address.) This is normally okay as we can use the
ceph.conf cluster_network and public_network variables to force the
monitor to listen on the addresses we want. However, we also need
ansible to set the correct monitor IP addresses in "mon hosts" (i.e. the
addresses the monitors will listen on!). This new monitor_address_block
setting tells ansible which IP address to use for each monitor.

Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>