MDEV-10751 - fix ipv6 detection test in MTR (aka make travis work)

[grooverdan]

based on a number of variants in https://travis-ci.org/grooverdan/mariadb-server/builds (10.2-travis_no_ipv6 branch) the current ipv6 detection isn't returning false on travis where there is no IPv6.

Here we do a bind (to the MTR baseport) rather than a connect to test. This seems to work correctly.

I submit this under the MCA.

[svoj]

Hi Daniel,

Thanks for your contribution. JIRA task has been created to track this pull request: https://jira.mariadb.org/browse/MDEV-10751

This task was added to 10.2.3 backlog, which is planned to be handled between 2016-09-22 and 2016-09-29.

Thanks,
Sergey

[vuvova]

pushed in 10.2, thanks

[grooverdan]

nice simplification too.

[ottok]

Thanks @grooverdan !

@vuvova There is still Failing test(s): main.ssl_ca in your commit:

• Red cross in your commit: https://github.com/MariaDB/server/commits/10.2
• Log: https://travis-ci.org/MariaDB/server/builds/164961334