Pass monitor_address_block to ceph-ansible for mon_host

Pass monitor_address_block to ceph-ansible for mon_host

The ip address which clients and other nodes use to connect to the
monitors is derived from the monitor_interface parameter unless
a monitor_address or monitor_address_block is given (to set mon_host
into ceph.conf); this change adds setting for monitor_address_block to
match the public_network so that clients attempt to connect to the mons
on the appropriate network.

Change-Id: I7187e739e9f777eab724fbc09e8b2c8ddedc552d
Closes-Bug: #1709485