merge docker-common and common defaults vars
merge docker-common and common defaults vars

Merge `ceph-docker-common` and `ceph-common` defaults vars in
`ceph-defaults` role.
Remove redundant variables declaration in `ceph-mon` and `ceph-osd` roles.

Signed-off-by: Guillaume Abrioux <30a9df5a0293a6108675377fa1673f7aa713f915@redhat.com>

ceph/ansible-ceph-osd