CI: UndefinedBehaviorSanitizer

We already run the CI with AddressSanitizers but should also run an entry with [UndefinedBehaviorSanitizer](https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html).

Also, if we [suppress]() some of the memory leaks in dependencies we might be able to check more backends in AddressSanitizer.

Check all but memory leaks: `-fsantize=address` with export:
```
export ASAN_OPTIONS=detect_stack_use_after_return=1:detect_leaks=0:check_initialization_order=true:strict_init_order=true:detect_stack_use_after_scope=1
```

We can also activate the python backend for address sanitizer checks, as long as we export the `LD_PRELOAD` path to the falsely hidden `asan` symbols: #479

For MPI-parallel checks, we might be able to write a [suppression file](https://releases.llvm.org/7.0.0/tools/clang/docs/AddressSanitizer.html#suppressing-reports-in-external-libraries), excluding the whole external lib.

Refs:
(clang ubsan) https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html
(gcc ubsan) https://developers.redhat.com/blog/2014/10/16/gcc-undefined-behavior-sanitizer-ubsan/
https://github.com/google/sanitizers/wiki/AddressSanitizer
https://github.com/google/sanitizers/wiki/AddressSanitizerExampleUseAfterReturn