Removed qiime_test_data_dir from QIIME config.

Also updated qiime_test_data-related error messages in all_tests.py.

Fixes #854.
Removed reference to qiime_test_data repo.

Fixes #852.
Script usage tests are now sorted before being run

On Mac OS X, this was already the case, but on Ubuntu (Jenkins runs) glob wasn't sorting the directories.

Fixes #853.
Merge pull request #855 from jrrideout/issues-852-853-854

A few fixes to qiime_test_data stuff
Merge branch 'master' of github.com:qiime/qiime into issue-833