This is mostly a straight port of devstack:lib/ceilometer with some
minor cleanups in the code. Notable changes include:
* default values are moved to devstack/settings
* all services provided by ceilometer are turned on by default, use
disable_service to turn them off
* mongod smallfiles is no longer used as it is not (apparently) used
with deb-based installs and there's a lot of water under the
bridge since then, so let's remove the complexity
* config handling is broken down into smaller sub-functions
* explicitly require python redis driver if needed, otherwise it
will not be available in a virtualenv
* install_ceilometermiddleware is not included, it is moved to
lib/swift
Change-Id: If36faa72b8c8d0f58a4ab5d02ed9cf92de3583b7