A python library for configuring ceph

This python module was originally part of a salt execution module for configuring
ceph on large clusters but it became clear that the code was reusable without
salt.

All methods in this module are intended to be atomic and idempotent. Some state
changes are in practice made up of many steps, but will verify that all stages
have succeeded before presenting the result to the caller. Most functions are
fully idempotent in operation so can be repeated or retried as often as
necessary without causing unintended effects. This is so clients of this module
do not need to keep track of whether the operation was already performed or not.
Some methods do depend upon the successful completion of other methods. While
not strictly idempotent, this is considered acceptable modules having
dependencies on other methods operation should present clear error messages.