Add LEIN_SUPPRESS_USER_LEVEL_REPO_WARNINGS

Can be used to suppress warnings about repositories in user level profiles.  Also
adds the list of profiles containing :repositories when not suppressed.
Add test cases for warn-user-repos and fix

Refactored warn-user-repos to take an argument to enable testing.

The tests are different depending on whether
LEIN_SUPPRESS_USER_LEVEL_REPO_WARNINGS is set or not.  This is not ideal, but
there doesn't seem to be a good way of altering the environment variables in
clojure.
Merge pull request #986 from hugoduncan/feature/add-repo-warn-suppression

Add LEIN_SUPPRESS_USER_LEVEL_REPO_WARNINGS