osdmap, mon: switch the params of print_tree()

osdmap, mon: switch the params of print_tree()

* change from
    print_tree(ostream*, Formatter*)
  to
    print_tree(Formatter*, ostream*)
  this is more consistent with other map's print
  functions. e.g.
    MDSMap::print_summary(Formatter *f, ostream *out)
* and in print_tree(Formatter* f, ostream* os),
  - `f` and `os` will be mutual exclusive.
  - will assert(0) if both of them are NULL.

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