Pull cherrypy from remote repository.

Testing Done:
mba=aurora=; PANTS_VERBOSE=1 PYTHON_VERBOSE=1 ./pants src/main/python/apache/thermos/observer/bin:thermos_observer

before:
Unsatisfiable: Cannot satisfy requirements: [PythonRequirement(cherrypy==3.2.2)]

after:
Wrote /Users/wickman/clients/aurora/dist/thermos_observer.pex

Bugs closed: AURORA-368

Reviewed at https://reviews.apache.org/r/20917/