sysvinit: allow custom cluster names

[aalba6675]

Squashed commit: improves #6726

Allows custom cluster names during system startup by emulating CLI.
In Red Hat (/etc/sysconfig/ceph) or Debian (/etc/default/ceph):

cluster=mycluster

is equivalent to /etc/init.d/ceph --cluster mycluster

conf=/etc/ceph/mycluster.conf
use_default_conf=0

is equivalent to --conf /etc/ceph/mycluster.conf

[loic-bot]

SUCCESS: http://jenkins.ceph.dachary.org/job/ceph/9674/

• SUCCESS http://jenkins.ceph.dachary.org/job/ceph/LABELS=centos-7&&x86_64/9674/

[tchaikov]

@aalba6675 you might want to prefix your commit message with "init-ceph: " or "init-ceph.in: ". and also add a "Signed-off-by" line at the end of the commit message, see https://github.com/ceph/ceph/blob/master/SubmittingPatches#L62 . more examples could be found using git log src/init-ceph.in

[aalba6675]

Done - could you review the commit again.

Improved comment, added signed off from my collaborator.

[loic-bot]

FAILURE: http://jenkins.ceph.dachary.org/job/ceph/9734/

• FAILURE http://jenkins.ceph.dachary.org/job/ceph/LABELS=centos-7&&x86_64/9734/

[loic-bot]

FAILURE: http://jenkins.ceph.dachary.org/job/ceph/9735/

• FAILURE http://jenkins.ceph.dachary.org/job/ceph/LABELS=centos-7&&x86_64/9735/

[b-ranto]

Is there any tracker issue associated to this PR? I'd like to (propose to) see this PR backported to hammer -- I had a bug report regarding this for Fedora 22 (hammer inside).

[gregsfortytwo]

I've got a related set of patches in wip-init-names that have been languishing since earlier this year — making sysvinit support multiple (named) clusters on a single host. The bit I ran into there is that we need to handle upgrading properly.
This patch is a little simpler (it's not touching the pid filenames) and so might work, but please check upgrades against it!

[liewegas]

@BRANTO1 There isn't a tracker issue (not really a bug). Mind just opening a PR with a cherry-pick -x against hammer?