Add ssl connection support [MYSQL]

This make pool works when adding SSL support to DATABASES:
Mysql SSL config sample:
DATABASES = {
'default':{
...
   'OPTIONS': {
            'ssl': {
                'ca': PROJECT_PATH + '/certs/ca.pem',
                'cert': PROJECT_PATH + '/certs/cert.pem',
                'key': PROJECT_PATH + '/certs/key.pem'
            },
        }
}
Merge pull request #6 from danigosa/master

Add ssl connection support [MYSQL]