stable 3.1 igw: enable and start rbd-target-api
stable 3.1 igw: enable and start rbd-target-api

Backport
https://github.com/ceph/ceph-ansible/pull/2984
to stable 3.1.

From upstream commit:

commit 1164cdc002cccb9dc1c6f10fb6b4370eafda3c4b
Author: Guillaume Abrioux <gabrioux@redhat.com>
Date:   Thu Aug 2 11:58:47 2018 +0200

    iscsigw: install ceph-iscsi-cli package

installs the cli package but does not start and enable the
rbd-target-api daemon needed for gwcli to communicate with the igw
nodes. This just enables and starts it.

This fixes Red Hat BZ
https://bugzilla.redhat.com/show_bug.cgi?id=1613963.

Signed-off-by: Mike Christie <39daeb1549a929782e38aa87c4e3da7f3844b09a@redhat.com>

fgal/ceph-ansible,fgal/ceph-ansible