Unable to start or pull (broken tag?)

[JCGoran]

This is on the latest master (commit 2008cbb), with git 2.30.1.
Basically, running ./xfce-test start fails with:

Starting container: Unable to find image 'schuellerf/xfce-test:master' locally
docker: Error response from daemon: manifest for schuellerf/xfce-test:master not found: manifest unknown: manifest unknown.

Ditto for ./xfce-test pull (./xfce-start pull [TAG] works though).
Debugging the script with set -x reveals that it sets TAG=master using git, but there's no such Docker tag on Dockerhub. Since the git tags do not necessarily correspond to the Dockerhub tags, I think this causes the above behavior.

Proposed fix

Compare the output of the get_tagsfunction with whatever the user provided for TAG, or use latest if it's unset.