Output from Examples

[Laurie Nevay]

Currently in bdsim/examples/CMakeLists.txt there is (now - was 'root')

set(TESTING_PERM_ARGS ${TESTING_PERM_ARGS} --output=rootevent)

This results in very very large numbers of output files accumulating in a build directory used for repeated testing.

Better we set the default to none and override explicitly when we want output to avoid accumulating test files that could be big.

Repeated executable arguments override previous ones, so this is ok.

[Laurie Nevay]

We should just clear the build directory entirely at the beginning of each build (ie on a testing platform). The behaviour is fine.