The `baseurl` variable in the template was misspelt as `base_url` when
the template was instantiated, resulting in LAVA jobs failing due to
the invalid URLs generated:

    Job error: Unsupported url protocol scheme:

Use `set -u` to ensure the shell loudly complains if we end up again
using a variable that has not been explicitly set.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>