Adding --p-logging-dir option

[mortonjt]

As discussed in #70 , we don't want to arbitrary save logging information in a default location (esp if it is running in qiita or something).

Having a --p-logging-dir option may be needed in order to pipe this information to /tmp if necessary. We'll want to avoid the option of completely disabling logging if possible (too much code will have to change).

@antgonza , feel free to qiime in.

[antgonza]

Thank you for reaching out. This solution should work for Qiita but I think we might need to do some extra steps to add this directory to the actual output artifact ... but that can be done once this is added. 😉