ceph-disk: enable --runtime ceph-osd systemd units

ceph-disk: enable --runtime ceph-osd systemd units

If ceph-osd@.service is enabled for a given device (say /dev/sdb1 for
osd.3) the ceph-osd@3.service will race with ceph-disk@dev-sdb1.service
at boot time.

Enabling ceph-osd@3.service is not necessary at boot time because

   ceph-disk@dev-sdb1.service

calls

   ceph-disk activate /dev/sdb1

which calls

   systemctl start ceph-osd@3

The systemctl enable/disable ceph-osd@.service called by ceph-disk
activate is changed to add the --runtime option so that ceph-osd units
are lost after a reboot. They are recreated when ceph-disk activate is
called at boot time so that:

   systemctl stop ceph

knows which ceph-osd@.service to stop when a script or sysadmin wants
to stop all ceph services.

Before enabling ceph-osd@.service (that happens at every boot time),
make sure the permanent enablement in /etc/systemd is removed so that
only the one added by systemctl enable --runtime in /run/systemd
remains. This is useful to upgrade an existing cluster without creating
a situation that is even worse than before because ceph-disk@.service
races against two ceph-osd@.service (one in /etc/systemd and one in
/run/systemd).

Fixes: http://tracker.ceph.com/issues/17889
Signed-off-by: Loic Dachary <loic@dachary.org>
(cherry picked from commit 539385b143feee3905dceaf7a8faaced42f2d3c6)