Rewrite http_requests to use postProcessor API

Both the control and experiment tests can be rescheduled independently
if we use the postProcessor API.
Use inlineCallbacks

For some reason, using inlineCallbacks seems to produce a proper result
from the doRequest method -- however, in the previous code the returned
deferred had been called but the result was not set.
Revert "Refactor the code of the post processor to work properly."

This reverts commit e89163c608f27cd34cd871b6bcb814a24b65c762.
Add measurement result to measurement object.

Simplify callback chain by adding the measurement result to the measurement object.
Refactor postProcessor to accommodate result callback refactoring.
Revert "Do not raise an exception on no input processor."

This reverts commit 77cfa98526f43919619dacf27a0f5c2644313985.