glossary: normalize usage of upper/lower/capitalization
glossary: normalize usage of upper/lower/capitalization

* Use lower case by default
* Use upper case for abbreviation
* Use capitalization for proper nouns like OpenStack service names

The basic policy follows OpenStack manuals glossary.

Change-Id: I44318cbeeb0cc7f7ccc249e383328e6e8f592f77

openstack/i18n,openstack/i18n