Simplify docs build

Remove unnecessary old code from tools/build_docs.sh; it now only builds
docs for the current branch in the current working directory.

Fix the merging if the git log changes into changes.html.

Change-Id: I965dc3383b6317807ca0d47fe42648a19e96b57b
Sort oslo libraries and add missing oslo.context

Ensure both lists of oslo libraries are sorted and
add the missing oslo.context in install_oslo method

Change-Id: I5b849c97b681e65425304e05534a61140e4e1fda
Document local.conf settings for ceilometer

Describe the various settings that can be made to control the
behavior of Ceilometer. Doing in lib/ceilometer for now. When there
is more something under doc may be warranted.

Change-Id: I9cd47085a5e91bae0a88f6e26f6c8bdc86c02978
Merge "Document local.conf settings for ceilometer"
Merge "Simplify docs build"
Merge branch 'master' of https://github.com/openstack-dev/devstack