catch IPClusterEngine up with changes to LocalEngine

s/_do_initialize2/_do_initialize/
s/_do_analyze2/_do_analyze_with_summary/
add summary_func_every_N argument to get_analyze_arg_tuples override

separately: allow config_filename constructor argument to default to None (local ipcluster)
by default, use _do_analyze_with_summary

handle summary_func_every_N default value of None