[BUG] mysql returner: MYSQLdb use 'latin-1' encoding by default but tables are utf-8

Description
When using mysql returner, there's a traceback when saving some events because MYSQLdb use 'latin-1' encoding by default but tables are utf-8.

Setup
A simple master minion setup with a database.

Steps to Reproduce the behavior
try to run sys.list_functions, sys.doc, sys.list_runner_functions and sys.runner_doc on the minion.

master_1  | 10:33:38 master.1 | [ERROR   ] Error in function _return:
master_1  | 10:33:38 master.1 | Traceback (most recent call last):
master_1  | 10:33:38 master.1 |   File "/usr/lib/python3/dist-packages/salt/master.py", line 1839, in run_func
master_1  | 10:33:38 master.1 |     ret = getattr(self, func)(load)
master_1  | 10:33:38 master.1 |   File "/usr/lib/python3/dist-packages/salt/master.py", line 1638, in _return
master_1  | 10:33:38 master.1 |     self.opts, load, event=self.event, mminion=self.mminion)
master_1  | 10:33:38 master.1 |   File "/usr/lib/python3/dist-packages/salt/utils/job.py", line 108, in store_job
master_1  | 10:33:38 master.1 |     mminion.returners[savefstr](load['jid'], load)
master_1  | 10:33:38 master.1 |   File "/var/cache/salt/master/extmods/returners/mysql.py", line 362, in save_load
master_1  | 10:33:38 master.1 |     cur.execute(sql, (jid, salt.utils.json.dumps(load)))
master_1  | 10:33:38 master.1 |   File "/usr/lib/python3/dist-packages/MySQLdb/cursors.py", line 207, in execute
master_1  | 10:33:38 master.1 |     args = tuple(map(db.literal, args))
master_1  | 10:33:38 master.1 |   File "/usr/lib/python3/dist-packages/MySQLdb/connections.py", line 304, in literal
master_1  | 10:33:38 master.1 |     s = self.escape(o, self.encoders)
master_1  | 10:33:38 master.1 |   File "/usr/lib/python3/dist-packages/MySQLdb/connections.py", line 226, in unicode_literal
master_1  | 10:33:38 master.1 |     return db.literal(str(u).encode(unicode_literal.charset))
master_1  | 10:33:38 master.1 | UnicodeEncodeError: 'latin-1' codec can't encode character '\u2019' in position 73212: ordinal not in range(256)
master_1  | 10:33:38 master.1 | [ERROR   ] Could not store events - returner 'mysql.event_return' raised exception: 'latin-1' codec can't encode character '\u2019' in position 73469: ordinal not in range(256)

Expected behavior
No traceback pls.

Versions Report

Salt Version:
           Salt: 3000.1
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: 3.5.0
       dateutil: 2.5.3
      docker-py: Not Installed
          gitdb: 2.0.0
      gitpython: 2.1.1
         Jinja2: 2.9.4
        libgit2: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.6.2
   mysql-python: 1.3.7
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.5.3 (default, Sep 27 2018, 17:25:39)
   python-gnupg: Not Installed
         PyYAML: 3.12
          PyZMQ: 16.0.2
          smmap: 2.0.1
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.2.1
 
System Versions:
           dist: debian 9.11 
         locale: UTF-8
        machine: x86_64
        release: 5.5.15-200.fc31.x86_64
         system: Linux
        version: debian 9.11 

MYSQLdb should be forced to use 'utf-8' as an encoding.
adding options:

charset="utf8",
use_unicode=True,

to the MySQLdb.connect function do the trick.

Start in the MySQL returner connection setup, then trace the save_load path shown in the traceback. Reproduce the issue with the listed sys commands and verify that events containing non-Latin-1 characters are stored without a traceback when the connection uses the requested UTF-8 options.