removed global_cleanup from Extensions to RunnableDB. Now RunnableDB subclasses

don't have any ensembl-hive extensions.  To get access to extended hive functionality
one must inherit from Hive::Process.  A multiple inheritance is allowed like:
  our @ISA = qw( Bio::EnsEMBL::Hive::Process Bio::EnsEMBL::Pipeline::RunnableDB );