doc: fix ceph-installer(8) title formatting
doc: fix ceph-installer(8) title formatting

Prior to this change, rst2man would break "ceph-installer" and the
longer description onto two lines:

  ceph-installer -

  A  command line utility to install and configure Ceph
  using an HTTP API as a REST service to call Ansible.

Reformat so that the name and description will appear on the same line
in the nroff man page source:

  ceph-installer - Command line utility to install and configure Ceph
  using an HTTP REST API

ceph/ceph-installer,ceph/ceph-installer,ceph/ceph-installer,ceph/mariner-installer