This replaces a previous (now closed) PR:
https://github.com/galaxyproject/galaxy/pull/8279
A few changes:
- tests for code in galaxy/tool_util moved under test/unit/tool_util
- common parts (used in both tools and tool_util) factored out into
unittest_utils/sample_data.py
- symlink to sample_data.py in test/unit/tool_util/ is needed to make
the tool_util package tests run. This is not an ideal solution, but it
avoids duplication of the sample data used by tests in tools/ and
tool_util/.
