Ansible role supports setting besu_version=='latest' and role discover the latest released version from the GitHub repository. Since the besu_version may be set via command line, this variable cannot be updated using the set_fact. Introduced a new variable _besu_version which is updated to either value of besu_version or latest version discovered
Signed-off-by: Chaminda Divitotawela <cdivitotawela@gmail.com>