strip trailing forward slash on recrusive cp for darwin
strip trailing forward slash on recrusive cp for darwin

 - fixes systests on darwin where previously the recursive cp would fail
   due to everything being copied after the last forward slash.
   Specifically, everything in  `systest/all_SUITE_data/` would be
   copied but not `all_suite_data` dir itself which the tests expected.

saleyn/rebar3,rebar/rebar3,lrascao/rebar3,ferd/rebar3,tsloughter/rebar3,rebar/rebar3,erlang/rebar3,djnym/rebar3,vladdu/rebar3