This change specifies the absolute path to the benchcab executable in
the job script so that we don't run into path issues when running using
a 'locally installed' version of benchcab. This will be helpful making
code changes and testing them on NCI.

Fixes #95

We should not use a default value when trying to infer the path to the
benchcab executable. If the path is undefined, we raise an exception as
this is likely a sign that the user's PATH variable is configured
incorrectly.

Co-authored-by: Claire Carouge <[email protected]>