Avoid double negatives in the run tests shell script to make things clearer

[jatkinson1000]

Should resolve #259

Moves X_ONLY to RUN_X and now checks:

if [ "${RUN_X}" = true ]; then
  cd "${BUILD_DIR}/test/x"
  ctest "${CTEST_ARGS}"
  cd -
fi 

[jwallwork23]

Oh, I guess I misunderstood but I thought you were going to change the actual argument too? Although I guess that'd beg the question of what the default options would be.

An alternative would be to split the test script into two- one for the unit tests and one for the integration tests?

[jwallwork23]

I think you might want to do an interactive rebase, dropping commits from #222.

[jatkinson1000]

I was envisaging it going in after #222, but actually you are correct, could go in now at the expense of you perhaps needing to update 222.

[jwallwork23]

Okay cool, thanks!