Unwind InvocationTargetException failures when accessing the repository

If during repository startup an exception occurs the exception will be catched in the HippoRepositoryFactory as InvocationTargetException.

Currently it assumes there is only a single layer of reflection based invocation, and re-throws only the intial (top level) cause of the InvocationTargetException.

But if within the repository startup the exception occurs in a further nested level of reflection based invocations, the re-thrown exception still might be of type InvocationTargetException, which will produce unnecessary noise in the logging, which also is more difficult to digest than unnecessary.

Fix is simple: just keep unwinding the InvocationTargetException until the first non-InvocationTargetException based cause is found.