Switch to using mysqlclient instead of MySQL-python as a dev dependency.

Review Request #9671 — Created Feb. 18, 2018 and submitted — Latest diff uploaded

Information

Djblets
release-1.0.x
0b126c5...

Reviewers

MySQL-python hasn't really been maintained in a while, is not
compatible with Python 3, and isn't really getting a whole lot of
updates. The successor to this package, which is fully API-compatible,
has wheels, and is compatible with Python 2.7 and 3, is mysqlclient.
This switches our development dependency over to that.

Successfully installed via pip and easy_install on Python 2.7, 3.4,
3.5, and 3.6. MySQL-specific unit tests passed with this dependency
(as did Django Evolution tests for MySQL, which is a better set of
tests in this case).