Minor Description
Per discussion in some recent code reviews (http://gerrit.ent.cloudera.com:8080/#/c/1531/ in particular) the Env class is sort of confusing what it is for – if it's for mocking only, then we should get rid of some of the pieces that are never mocked/substituted. If it's for platform portability then we probably should have a separate env_linux for linux-specific (non-posix) stuff. This JIRA is to clean up that mess.