The execution word/term is not the most fortunate as used in DTS, as it has a
pretty well established meaning outside of DTS. This creates confusion, so
let’s rename it to something better.

We should also agree on what do we call a full DTS run. That could just be a
DTS run. A part of the run (the current execution) could be a sub-run (a
sub-run would then be a testbed with testcases). Other possible words could be
job, testbed-run (the execution would be renamed to testbed in this case).