ceph.spec.in: disable lttng and babeltrace explicitly

ceph.spec.in: disable lttng and babeltrace explicitly

before this change, we do not pacakge tracepoint probe shared libraries
on rhel7. but "configure" script enables them if lttng is detected. and
rpm complains at seeing installed but not pacakged files. as EPEL-7 now
includes lttng-ust-devel and libbabeltrace-devel, we'd better
BuildRequire them, and build with them unless disabled otherwise. so in
this change
* make "lttng" an rpm build option enabled by default
* BuildRequire lttng-ust-devel and libbabeltrace-devel if the "lttng"
 "lttng" option is enabled
* --without-lttng --without-babeltrace if the "lttng" option is disabled

Fixes: #14844
Signed-off-by: Kefu Chai <kchai@redhat.com>