tests/auc: change back to python3

Change the interpreter of the python script back to python3, as it was
when the script was initially added in
Idff9d757ab956179aa41ada2a223fd9f439aafbd. In the meantime, it had been
changed to python2 to make it work with build slaves that were missing
python3, but this is not necessary anymore.

This should be merged shortly after osmo-python-tests was migrated to
python3, and the jenkins build slaves were (automatically) updated to
have the new osmo-python-tests installed.

Related: OS#2819
Depends: osmo-python-tests I3ffc3519bf6c22536a49dad7a966188ddad351a7
Change-Id: Ifbb8f8f5428657a1c2d4d6d1217f8e374be43aba
2 files changed