The logic that genates the list of commits to submit for a review

request with commit history was previously attempting to naively convert

the the revisions (which were text) to bytes. This is fine on Python 2,

where bytes(s) implies s.encode('ascii') but this is no longer the

case on Python 3. Instead, str.encode() must be called and it must be

provided with a codec. This method works on both Python 2 and Python 3.

Confirmed the following on Python versions 2.7, 3.5, 3.6, and 3.7:

With this entire patch stack (/r/10685, /r/10695, and /r/10697),

rbt post is able to create review requests with commit history.