reintroduce previously exported riak_core_coverage_plan:create_plan/5
reintroduce previously exported riak_core_coverage_plan:create_plan/5

jdaily has changed the arity of create_plan from 5 to 6 in a8fac2868e.

As this is an exported API function, its callers will be affected, hence
this fix.

Kyorai/riak_core