Migrate testing related third parties to /appengine/third_party_local/.

These third parties are not used nor uploaded to the AppEngine instances. They
were under /appengine/components/ but I think it's worth raising at higher
level. More importantly, the name is intentionally 'third_party_local' to make
it clear that these packages are never to be uploaded to AppEngine. This gets
rid of the confusion between components/third_party and

Removed a few sys.path manipulation along the way and renamed appengine/README
to README.md.

Imported libraries will be migrated in a follow up.


Review URL: https://codereview.appspot.com/217190043
76 files changed