Rename getContainerIDsOfEnv to getContainerIDsOfShaEnv, since that's what it is.
Handle tearing down containers by env without sha properly.

Also add a TODO that this whole logic chain is broken.
go fmt.  I appear to have forgotten this step on some past commits.
Merge pull request #27 from ooyala/fix-teardown-env-without-sha

Handle tearing down containers by env without sha properly.