supervdsm: enable coredumping

Enable coredump both on el6 (sysvinit)
and on el7 (systemd).
Also, limit core size to 0 in case of
enable_core_dump is set to False

Change-Id: Id877e77046dd636c625e5043e358537c07b5beee
Bug-Url: https://bugzilla.redhat.com/1167814
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Signed-off-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/35480
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dima Kuznetsov <dkuznets@redhat.com>