Fix unclosed socket on constructor (connection) failure

[vtermanis]

Creating a Connection instance (with use_pure=True) and e.g. specifying an invalid password causes a ResourceWarning (if running python 3 with -b flag) as the underlying socket is not closed in such a case. This patch addresses this problem.

[mysql-oca-bot]

Hi, thank you for your contribution. Please confirm this code is submitted under the terms of the OCA (Oracle's Contribution Agreement) you have previously signed by cutting and pasting the following text as a comment:
"I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it."
Thanks

[vtermanis]

I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

[mysql-oca-bot]

Hi, thank you for your contribution. Your code has been assigned to an internal queue. Please follow
bug http://bugs.mysql.com/bug.php?id=82324 for updates.
Thanks

[nmariz]

Hi Vilnis,
Can you provide more details about your setup? I've tested with Python 3.5 and MySQL 5.7.18 and I could not replicate the issue.

[vtermanis]

Testing against 10141444881c7ae583 (current head of master branch) I can reproduce the issue with the following code (where either the user is unknown or password is invalid):

from contextlib import closing
from mysql.connector import connect

def main():
    with closing(connect(
        host='localhost',
        user='unkown',
        password='invalid',
        use_pure=True
    )) as conn:
        # Doesn't get here obviously due to "Access denied"
        pass


if __name__ == '__main__':
    main()

.. and then running it using (I tested with Python v3.5.2 & MySQL 5.7.18 under Ubuntu):
python3 -Wall -b example.py

You should see below the access denied exception something like:

sys:1: ResourceWarning: unclosed <socket.socket fd=3, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('127.0.0.1', 36970), raddr=('127.0.0.1', 3306)>

[nmariz]

Thanks Vilnis, I just verified it using Python 3.5.2.
Python 3.5.0 does not emit this warning.