crush: add adjust_subtree_weight()

Adjust the weight for all (leaf) items beneath a subtree.

Signed-off-by: Sage Weil <sage@inktank.com>
mon/OSDMonitor: add 'osd crush reweight-subtree ...'

Reweight all items within a subtree.  For example, you might reweigh tall
OSDs within a rack to a new value.

Signed-off-by: Sage Weil <sage@inktank.com>
mon/OSDMonitor: simplify 'osd crush reweight ...' flow

Use the goto labels; drop the do/while.

Signed-off-by: Sage Weil <sage@inktank.com>
doc: fix typo in erasure coding section

Signed-off-by: Venky Shankar <vshankar@redhat.com>
Merge pull request #1940 from vshankar/doc-fix

doc: fix typo in erasure coding section

Reviewed-by: Loic Dachary <loic@dachary.org>
Merge pull request #1872 from ceph/wip-reweight-tree

mon: add 'osd crush reweight-tree ...'

Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>