Fix failing specs with consistent request_id

Some specs are failing[1] because the expected and returned input have different request ID's. Fixing by ensuring Punchblock always returns the same ID, as is done in the Punchblock specs[2].

[1] https://travis-ci.org/adhearsion/matrioska/builds/38971352
[2] https://github.com/adhearsion/punchblock/blob/develop/spec/spec_helper.rb#L28-31