toaster-manual: change mysql driver

toaster-manual: change mysql driver

Here is a quote from Django 1.9 documentation regarding this:
mysqlclient is a fork of MySQLdb which notably supports Python 3
and can be used as a drop-in replacement for MySQLdb. At the time
of this writing, this is the recommended choice for using MySQL
with Django.

(From yocto-docs rev: deb02aeea4912f9d7978de3529467e4503eeeffb)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>