[WIP] Refactor test_updater.py and repository_setup.py.

Add generate.py script and pre-generated repository files used by Unit tests (replacing repository_setup.py).
Refactor test_updater.py (10 test cases remaining).
[WIP] Refactor test_updater.py

Continue refactoring the test cases of test_updater.py.
Fix issue where repository_tool.py was not writing new compressed metadata.
Minor edits to TUF modules.
Merge branch 'develop' of https://github.com/vladimir-v-diaz/tuf into develop
Finish refactor of test_updater.py.

test_updater.py now uses repository_tool.py to update the remote repository as needed, and no longer depends on mocking and repository_setup.py.
Remove obsolete helper functions.

Minor edits to comments.
Move repository data to 'tuf/tests/repository_data'
Merge branch 'develop' of https://github.com/theupdateframework/tuf into develop
Re-add comment about disabling password confirmation in repository_tool.py.
Merge pull request #189 from vladimir-v-diaz/develop

Refactor test_updater.py