Only deploy snapshots on non-tagged builds

Workaround unexpected `tags: false` behaviour. See:
https://github.com/travis-ci/travis-ci/issues/2378
Add non-existent deploy dir fail safe

Closes item:560
Merge deploy targets

Create both build type directories, taking advantage of the fact that we know
one will be empty.
Merge pull request #354 from tlvince/bug/travis-release-deploy

Fix release build deploys, closes item:560