zpm: rename a variable in `deploy_project`

Instead of `version`, the variable is renamed to `ui_auth_version`. The
difference here is subtle, because the auth version is used in two ways
in zpm:

1) To authenticate to Swift/ZeroCloud services
2) To populate auth information in UI templates of zapps (at deploy
   time)

The first is determined within the `_get_zerocloud_conn`. The second can
also be determined within `_get_zerocloud_conn`, but can be overridden
by the `--no-ui-auth` command line arg.
zpm: add `_guess_auth_version` function
zpm: integrate `_guess_auth_version`

Currently, only deploy and execute require authentication.
commands: refactor the default auth version stuff

Instead of specifying the default in the command line arg definition,
this is handled else where (see _get_zerocloud_conn and
_guess_auth_version).
test_zpm: improve coverage for _get_zerocloud_conn
Merge pull request #176 from larsbutler/deduce-auth-version

Deduce auth version (from cmd line args / env vars)