Description of problem:
The current implementation of retrace-server uses mock exclusively for userspace cores.  There's been various issues pointed out with mock which are significant for interactive mode:
https://bugzilla.redhat.com/show_bug.cgi?id=1153304#c0

Version-Release number of selected component (if applicable):
retrace-server-1.15-1.el6.noarch

How reproducible:
Every time

Steps to Reproduce:
1. Queue a userspace core through the manager page

Actual results:
mock is used with no option to use docker

Expected results:
mock is configurable plugin so docker can be used

Additional info:
Kyle has done some work on this and I believe Jakub may have some design at least in mind as well, though I don't think any has a proof of concept implementation yet.

This is likely to require extensive patches though in my opinion it is a worthwhile effort to be able to use docker.