Choose specific python version

These RPMs contain problematic shebang in some of the scripts:

mariadb-test-10.2.9-3.fc27

 * Scripts containing `#!/usr/bin/env python` shebang:

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_bin.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_bin_rename.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_char.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_char_binary.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_char_charbinary.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_char_rename.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_int.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_int_key.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_int_not_supported.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/change_column_int_rename.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/fast_update_blobs.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/fast_update_blobs_fixed_varchar.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/fast_update_blobs_with_varchar.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/fast_update_decr_floor.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/fast_update_int.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/fast_update_varchar.py

   /usr/share/mysql-test/plugin/tokudb/tokudb/t/fast_upsert_int.py

This is discouraged and should be avoided. Please check the shebangs

and use either `#!/usr/bin/python2` or `#!/usr/bin/python3`.

Read the following document to find more information and a possible cause:

 https://pagure.io/packaging-committee/issue/698

Or ask at #fedora-python IRC channel for help.

If you think the result is false or intentional, file a bug against:

https://github.com/fedora-python/task-python-versions/issues