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>
(cherry picked from commit f1a44907a2f83cb8080cd8ab5980a30306a33fbd)

Conflicts:
	ceph.spec.in: trivial resolution, the context changed
        (other packages, files etc.) but the semantic did not