Add possibility to execute arbitrary scripts after test execution

[S7evinK]

This can be useful to extract coverage logs or database files to further examine failing tests.

Example script:

#!/bin/bash

echo "Params: $@";

if [[ $3 == "false" ]]; then # test passed, do nothing
  exit 0
fi

mkdir -p /tmp/complement/coverlogs/$2/$1/

docker cp $1:/dendrite/integrationcover.log /tmp/complement/coverlogs/$2/$1/

This would copy /dendrite/integrationcover.log from within the container (e.g. d9c4d433e2d77f1a2572933e738f3681bce1aab1404a2ce756c8f2bb4ffffbbc) to something like /tmp/complement/coverlogs/TestContent/d9c4d433e2d77f1a2572933e738f3681bce1aab1404a2ce756c8f2bb4ffffbbc/integrationcover.log