tools/rados: call pool_lookup() after rados is connected

tools/rados: call pool_lookup() after rados is connected
This commit fixes a segmentation fault when using --pgid
option in rados ls command in combination with --pool/-p option.
The reason for the crash was that we can not use the rados object
before connecting it with the cluster using rados.init_with_context().

Fixes: https://tracker.ceph.com/issues/41875
Signed-off-by: Vikhyat Umrao <vumrao@redhat.com>
(cherry picked from commit 56b6dd9bd7a50371062128122e6a899f2c79c5f5)

Conflicts:
	src/tools/rados/rados.cc