client: Refactor view checking for operations.

This commit introduces a new abstraction for operations that can result in an
InvalidViewException. Each of those operations will be encapsulated by an
executor function which checks for InvalidViewExceptions, renews the view and
retries the operation.
client: Refactor UUIDContainer handling.

Since the XLocSet can change during the lifetime of an ContainerUUUIDIterator
it has to be ensured, that the references to UUIDUItems remain valid until the
last iterator has been destroyed.
libxtreemfs for Java: Adjust invalid view handling to the c++ client.