…gned certificates

The tests assumption that certificates in the ROOT store are all self
signed does not hold anymore.

Use system property java.home in favor of environment variable
JAVA_HOME to register the windows service.

… workaround

- Advapi32#DecryptFile can be called on read-only file
- Secur32Test is unstable with ImpersonateSecurityContext, splitting it
  into separate test improves stability
- Fix IPHlpAPITest#testGetUdpStatistics - the statistics that is
  returned can be inconsistent

malloc does not clear the memory it allocates and thus random data can
be present. It was observed, that cleanup routines assume, that fields
not holding NULL need to be freed for example. That is not true if the
field was not cleared on allocation. One such example was
callback->arg_classes in free_callback.