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.
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.
Indicate whether Tor was used in a request or not in the report.