Allow any conditional branching opcode to have both paths included in a region

Summary: We were artificially limiting the control flow within regions to come
from JmpZ/JmpNZ, but there's no good reason for that.  So, let's lift the
restriction.

Reviewed By: @alexmalyshev

Differential Revision: D1445273
Bump timeout more, retry on server out-of-date

Summary: 300s was chosen because it was the p90 of hack server startup times
as observed here: https://fburl.com/29184831

Reviewed By: pad, eladg

Differential Revision: D1449428