Add derived_from to scrooge_gen scrooge generated targets

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/33099414

Reviewed at https://rbcommons.com/s/twitter/r/926/
filter tests:: --filter-ancestor=-blacklist:blacklist ain't working. try to fix

add a test for this case

the problem: at the time the ancestor filter does its thing, the blacklist:blacklist target doesn't "realize" it has deps. My hazy understanding: we added blacklist:blacklist to the build graph, but didn't tell it to, uhm, recurse its deps. I think this change tells it to recurse its deps. And I guess that's what we want here. But I don't necessarily know about better approaches, silly repercussions, etc.

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/33097382

Bugs closed: 506

Reviewed at https://rbcommons.com/s/twitter/r/925/
test improvement: make sure that the thing we're filtering out is there

because if it's not there in the first place, then "filtering" it isn't so reassuring

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/33117007

Reviewed at https://rbcommons.com/s/twitter/r/928/
Make ./pants goal targets to find all the targets aliases/types automatically instead of being hardcoded.

Currently in TargetsHelp, we hardcoded the list of target aliases to target types mapping. This RB changes it to make the discovery dynamically, by looking at all the registered aliases in build_configuration and then intersect them with all the installed target types from SourceRoot.

Testing Done:
passed: PANTS_DEV=1 ./pants goal test tests::

Bugs closed: 333

Reviewed at https://rbcommons.com/s/twitter/r/796/
Cleanups for import unittest/unittest2

This change was made mechanically using sed, except for some manual edits in
test_build_graph.py and test_thrift_util.py

(I realize this change will be pretty much a no-op after we drop python 2.6 support)

Testing Done:
CI is running @ https://travis-ci.org/pantsbuild/pants/builds/32971877

Bugs closed: 500

Reviewed at https://rbcommons.com/s/twitter/r/919/
Fix credentials fetching during publishing

Reviewed at https://rbcommons.com/s/twitter/r/901/