Fixed bug due to Hazard Pointer.
HelpScan was implemented wrong -> Scan could be executed be different threads the same time -> FixedSize lists got messed up -> program tried to return wrong pointers to the object pool -> segfault or hang

Moreover, added assertion that checks that only one thread concurrently enters scan, for avoiding these kind of bugs in the future.
Merge branch 'development' of https://github.com/siemens/embb into development