ceph: show basic help before initializing cluster connection

That way we still get help if there is an error.

Signed-off-by: Sage Weil <sage@inktank.com>
ceph: catch exceptions thrown during the rados handle init

In my case, making ceph.conf unreadable triggers an exception here:

Traceback (most recent call last):
  File "./ceph", line 802, in <module>
    sys.exit(main())
  File "./ceph", line 575, in main
    conf_defaults=conf_defaults, conffile=conffile)
  File "/home/sage/src/ceph/src/pybind/rados.py", line 221, in __init__
    self.conf_read_file(conffile)
  File "/home/sage/src/ceph/src/pybind/rados.py", line 272, in conf_read_file
    raise make_ex(ret, "error calling conf_read_file")
rados.Error: error calling conf_read_file: errno EACCES

Signed-off-by: Sage Weil <sage@inktank.com>