cthulhu: spelling, log boilerplate errors in pool_request_factory.py

Signed-off-by: Dan Mick <dan.mick@inktank.com>
cthulhu: set appropriate min_size on pool create/update

Use an algorithm similar to Ceph's: requested min_size or
default, compare to size, use whichever is smaller; or if
no requested *or* default, use size - size/2.

On update, only recalculate min_size if size or min_size is given.

Fixes: #8820
Signed-off-by: Dan Mick <dan.mick@inktank.com>
tests: try several pool min_size updates relative to size

Signed-off-by: Dan Mick <dan.mick@inktank.com>
doc: note special handling of min_size in pool create/modify

Signed-off-by: Dan Mick <dan.mick@inktank.com>
doc: missing module level in manhole notes

Signed-off-by: Dan Mick <dan.mick@inktank.com>
doc: update restapi docs

Signed-off-by: Dan Mick <dan.mick@inktank.com>
Merge pull request #194 from ceph/wip-8820

Squashed series from wip-8820