Allow multipart orphan cleanup to be run from command line

In the release notes for 1.5.0 in the comments about upgrading we have the instructions that require attaching to the console and calling an erlang function:

> * run riak_cs_console:cleanup_orphan_multipart/0 or riak_cs_console:cleanup_orphan_multipart/1 in an attached console to cleanup all buckets

I think is easy enough to go ahead and add this to the command line tools in order to make it easier for users. This is just a suggestion and it could be done after 1.5.0 is released, but it should be very easy to do and better for users.

cc: @michellep